CONTENTS: Parchment // Scribal Ink // Kulmus: The Sofer’s Pen // Ashkenazic, Sephardic, and Chassidic Script // The Divine Name Sha-dai // Surrounding Angels // Cosmic Runes // Halachic Measurement Units // Rambam’s Ten Principles // Reason for Top Third Placement // How to Measure the Top Third of a Doorpost // General Principles of Right-Hand Mezuzah Placement // Prayers and Customs
The Source of the Mitzvah
We are all familiar with the Torah sources for the mitzvah of mezuzah, as they are found in the first and second paragraphs of the Shema. Rambam lists the writing and placing of the mezuzah as the fifteenth positive commandment of the 613 Mitzvot. 
However, according to many authorities, the obligation to place a mezuzah on a rental or borrowed dwelling is Rabbinic.
The Hebrew phrase: “al mezuzot beitecha” is properly translated: “Upon the doorposts of your room”; the word “bayis” in Hebrew can refer either to a room or to an entire structure. Therefore, the halachah states that mezuzot must be affixed to every doorway that meets the prescribed criteria.
Unfortunately, many Jews miss out on this precious mitzvah, mistakenly believing that they fulfill their obligation by placing a mezuzah only on the main entrance to the house.
Mezuzot, like Torah scrolls and tefillin, must be written on specially prepared animal hides. Historically, the skins of goats, calves, sheep and even deer have been used. (You can snag an antique deerskin Torah scroll on eBay for just $49k!). Vellum, made from the skins of unborn calves, is prized for its smoothness and pliability. Some also suggest that since it has not yet entered into our corrupt world nor tasted its pleasures, it symbolizes spiritual innocence and purity. Until recently vellum was a rare commodity, but nowadays, the massive cattle ranges of the American Midwest provide “yippy-ay-oh” choice-grade vellum aplenty for scrolls worldwide. The animal does not need to be kosher slaughtered; it just needs to be from a kosher species.
Of course, the rawhide must be prepared for writing through a tanning process. According to present-day practice, the hides are first soaked in water and then tanned in limewash for several days until their hair falls off. They are then hung to dry, soaked again, and stretched on a wooden frame to dry.
A Jew must be physically involved in the process and have intention to dedicate the skins for their holy purpose. The extent of that involvement is a matter of halachic controversy; some authorities allow the use of machinery after a certain point, while others insist that it be purely hand-made. Because of these considerations and others, nowadays sofrim only write on parchment that is produced under rabbinic supervision.
Originally, after the tanning process, the outer hide (epidermis) was split from the inner fleshy skin (dermis) and the revealed surfaces were prepared for their various scribal purposes. This “splitting” is the reason why the Hebrew word for our parchment is klaf (split).
There are three layers of the split hide. The top layer just below the hair is called gvil, the layer beneath is called klaf, and the lowest layer, against the flesh, is called duchsustus. Torah scrolls may be written on gvil or klaf, although the use of gvil for Torah scrolls is very uncommon today. Tefillin and mezuzahs are written exclusively on klaf.
Nowadays, for a variety of reasons, the hide is not split. Rather, the soft flesh of the hide is scraped away, and the mezuzah script is written on the epidermis’ inner surface. 
The resulting parchment has a non-uniform, grayish surface with natural markings. Unfortunately, a great deal of cheap substandard mezuzot on the market are then “smeared” with glossy white paint to make it easier and quicker to write on them. Aside from the fact that many authorities do not consider such a coated mezuzah surface kosher to begin with, there is also the problem that once the parchment is folded to be put in a case, the coating usually cracks, destroying some of the letters and rendering the mezuzah “non-kosher.” Even if this does not happen immediately, eventually sunlight and humidity will almost surely cause this painted surface to dry and crack.
Not surprisingly, these cheap scrolls are usually written hurriedly and carelessly and do not pass halachic inspection. For these reasons and others, it is important to purchase one’s mezuzot and tefillin from a sofer or a reputable merchant. Caveat emptor!
The mysterious recipes for making the special ink used in the writing of mezuzot, tefillin and Torah scrolls sound like they come from one of the dusty old tomes of Potions Master Horace Slughorn, of Hogwarts renown. One might ask, “What’s wrong with using a Bic retractable ball-point goose quill?
From ancient tefillin and Dead Sea scrolls analyzed using a cyclotron at UC Davis, we can see that originally scribal ink was carbon based. Soot was gathered from burning vegetable fats, mostly olive oil. Charcoal dust was produced by burning vegetable matter such as beech trees or cedars. Often, a glass plate was suspended over the burning materials, and the gathered soot was scraped off for use.What’s clear in our tradition is that Moshe was told by G-d at Sinai that these holy items must be written with an ink called de’yo. It’s also clear that this de’yo must be black and must have staying power. The Zohar indicates that ideally its ingredients must derive from plants. Over millennia the technology used to achieve these outcomes has changed, but the principles remain the same.
Durability was achieved by adding oak gall nut powder, a substance rich in tannic acid, to “bite” into the parchment. The galls are formed when a gall wasp lays eggs on the leaves of oak trees. The hatched larvae feed upon the tree, secreting an irritant that prompts the tree to create a growth around the larva. This substance is still an important part of scribal ink today.
A gummy substance (now, gum arabic) was also added to keep all the ingredients evenly suspended in solution, improve the ink’s even flow from the reed or quill, and keep it from bleeding into the surface of the parchment. It also increases the brilliancy and gloss of the ink. Unfortunately, with time this substance dries and may cause the letters to crack.
Over the centuries, the secret of producing a durable ink made from carbon black has been lost. The Talmud itself records a halachic controversy regarding adding a chemical blackening agent (vitriol: ferrous sulfate) into the mix. Although the classic halachic sources recommend refraining from adding this ingredient, contemporary authorities have allowed its use as carbon-based ink alone is not a practical option.
Scribal ink is not holy, but all the ingredients involved in the production of mezuzot and other holy items must be kosher even though they are not consumed. Some researchers have asserted that commercial inks may contain problematic ingredients such as glycerin or shellac and are not an alternative to a traditionally made product for that reason alone. So, make sure your retractable goose quill is preloaded with the right stuff.
When we conjure up an image of a sofer plying his craft, we usually envisage a wizardly grey-beard with furrowed brows hunching over a scroll, writing cautiously with a graceful feather quill by candlelight. So it has been from time immemorial…
What’s wrong with this picture? The quill. In Biblical and Talmudic times, mezuzot, Torah scrolls, and other holy works were written using a reed pen. Even in our time, the reed pen remains the instrument of choice for many Sephardic scribes. In a fascinating passage, the Sages assert that the supple nature of the reed makes it the perfect match for the Torah:
A man should always be flexible as the reed, and let him never be unyielding as the cedar. And for this reason, the reed merited that of it should be made a pen for the writing of the Torah,
tefillin and mezuzot.
Some authorities rule that the “merit” derived from this consonance is an actual entitlement, allowing the reed to assert its moral rights over the quill. Nevertheless, the practical advantages of the quill, such as its ability to be carved with fine precision and retain its shape, has led to its acceptance in halachah and tradition. The softer reed requires constant sharpening. This time-consuming task decreases the sofer’s productivity and makes it more difficult to achieve uniform consistency of letter formation from the manually reshaped nib. Because Sephardic scrolls are often written with reed pens, their letters are noticeably thicker, and a specialist scribe is engaged to attach the spindly crowns (tagim) at their top.
Because all the processes in the production of mezuzot and other scrolls must be done with kosher materials, the plume of the graceful goose was used for centuries, but was later ousted by the hardier nib of the decidedly ungraceful turkey.
One might wonder why the turkey has merited that its quill should the obvious choice of the stainless-steel pen. Some authorities assert that just as the Torah does not allow the use of iron instruments used in war to sculpt the stones of the holy altar which brings peace, so too iron and steel pens should not be used to inscribe the holy words of Torah. In deference to this concern, there are those that suggest casing the nib in gold, which has no military association. In contrast, many do not agree that this analogy can be applied to scribal writing.
Plastic pens write quickly and precisely and are used by some scribes. But they tend to wear out quickly and are expensive to keep on replacing. More recently, the ceramic never-needs-sharpening “Kulmus Shamir” has come onto the market and has been adopted by some sofrim. But these options are not accepted universally, and there are those who insist on obtaining scrolls inscribed with traditional instruments. Nevertheless, for touch-up work and minor repairs, sofrim commonly use a metal-tipped rapidograph filled with traditionally made ink.
Remarkably, over the centuries and millennia of Jewish history, the text of Torah, tefillin, and mezuzot scrolls has remained remarkably the same — but different: There are subtle distinctions in the formation of many of the Hebrew letters in the scrolls of the various traditions of world Jewry.
It’s important to stress that all of these are merely variants of the original font, referred to as Ktav Ashuri. This is the font inscribed in the Tablets and written in the original Torah scroll of Moshe.  Although the status of ancient Paleo-Hebrew alphabet found on ancient Hebrew tomb inscriptions and coins is the subject of some discussion in the Talmud and commentaries, the accepted tradition is that the Ashuri script is the original holy font. All scribal writing today, in every community, is based on this font.
The Talmud does prescribe certain minimal forms for many of the letters and insists on precise adherence to several halachic criteria. For example, if a poorly formed letter resembles another letter too closely, it is disqualified. Also, if the ink of one letter merges with another letter, the resulting “blob” is not acceptable. In some cases, these mistakes can be rectified, but some errors can permanently render a mezuzah or tefillin scroll non-kosher.
Thankfully, since the differences found in the scrolls of the various traditions do not conflict with these criteria, most halachic authorities rule that a Jew of one tradition may fulfill his mitzvah with a scroll that accords with one of the other traditions. This mutual acceptance was articulated hundreds of years ago, and it has been affirmed by the contemporary Sephardic decisor Rabbi Ovadia Yosef and the Ashkenazic Rabbi Shlomo Zalman Auerbach, among many others.
However, these authorities also concur that, as in all halachic matters, a person should ideally strive to follow the custom of his community. Thus, one who is buying mezuzot should mention his tradition to the seller.
Ironically, the most common Ashkenazic script (Beit Yosef), was codified by the Sephardic author of the Shulchan Aruch, Rabbi Yosef Karo. In a reverse irony, Sephardic and Yemenite scrolls are written in a different script (called Velish), which is reported to be found also in Bohemia.
Yet a third script (Ktav Ari), follows the guidelines of the great kabbalist Rabbi Yitzchak Luria, Ha’Ari HaKadosh (1534-72). This script, a variant of Beit Yosef, has been adopted by most Chassidic communities. Although, as stated, most authorities maintain that this script is also kosher for Ashkenazic Jews, several contemporary decisors, including Chazon Ish, strongly question the acceptability of its variant form of the letter “צ”.
Three Hebrew letters peek out from the back of a mezuzah scroll, casting a spiritual aura on the room. שד-י (shin, dalet, yud). Sha-dai, pronounced in common speech Shakai to avoid overfamiliarity, is one of the Divine Names found in several verses of the Torah. Because nothing may be added to the prescribed verses written on the front side, it is inscribed on the back of the parchment. The Zohar teaches that the placement of the Name on the back symbolizes that Hashem should guard us from all sides. It also states that negative spiritual energies (mazikin) are repelled by the spiritual force emanating from the mezuzah and the Name.
This Divine Name symbolizes the power of the mezuzah to embrace a Jewish home with G-d’s presence and protection. The classical Torah commentaries interpret this Name in a variety of interesting ways, all of which shed light on its relevance to mezuzah.
Using this name, G-d introduces himself to Abraham (then still called Abram) when he commands him regarding the covenant of Brit Milah (circumcision):
And Abram was ninety-nine years old, and G-d appeared to Abram, and He said to him, “I am Ei-l Sha-dai; walk before Me and be perfect. And I will place My covenant between Me and between you, and I will multiply you very greatly (Genesis 17:1-2).”
Rashi paraphrases G-d’s words in this way: “I am He Whose G-dliness suffices for every creature.” [sheh = that, dai = is sufficient]. Therefore, walk before Me, and I will be your G-d and your Protector.” Similarly, that same Name, emblazoned on our mezuzah scrolls, broadcasts its message of Divine care and protection into the homes of Abraham’s grandchildren.
Others interpret this “sufficiency” in another way. They say that the Name symbolizes that we should be satisfied with the material possessions within our homes.
In contrast, the great Torah commentator Ramban asserts that this Name derives from a Hebrew word meaning “conquest.” He explains that G-d is assuring Abraham that He has the power to overcome the constraints of natural law and will bless him and Sarah with children in their old age. This supernatural event is symbolic of G-d’s covenantal promise to Abraham’s descendants that He will involve Himself with their destiny and not abandon them to the natural rise and fall of nations. Similarly, the Name on our mezuzot proclaims that one who enters a Jewish abode is stepping into a unique space of direct Divine providence where small miracles are the norm.
Rabeinu Bachya adds that whereas the nations are likely to attribute worldly events to materialistic forces and the whims of fortune, by placing mezuzot on our doorways, we proclaim that Hashem’s Providence surrounds us and governs our lives directly. 
Interestingly, we also form these same three letters when wrapping ourselves in tefillin. The letter shin is pinched into the leather of the head tefillin and wrapped on the back of our hand.
The dalet is wound around our palm and knotted into our head straps at the nape of the neck. The knot touching the arm tefillin is a yud.
As the Kitzur explains, these customs have developed as an expression of our love for Hashem, as we encounter His presence on the doorway of our home. Care must be taken that the mezuzah should not be treated as a mere lucky charm! In this spirit Rambam writes:
Thus, he will awake from his sleep and his obsession with the vanities of time, and he will recognize that there is nothing which lasts for eternity except the knowledge of the Creator of the world. This will motivate him to regain full awareness and follow the paths of the upright.
The ever-present mezuzah is also a reminder that even though in the innermost chambers of our home we may be hidden from human view, Hashem is aware of our deeds. The great kabbalist Rabbi Moshe Alshich of Tzefas explains:
When a person is away from the prying eyes of others, he may struggle to overcome his yetzer ha-ra. Therefore, Hashem commanded that we place a mezuzah on our doorways, so that as we enter our home, His presence will be in front of our eyes always, and we will not swerve from the proper path. For this reason, Hashem required that we place mezuzot on our innermost rooms.
Three unintelligible “words,” comprised of fourteen Hebrew letters, can be seen written upside-down on the back of a mezuzah scroll: כוזו במוכסז כוזו. These letters are actually an encrypted form of the Divine names written in the third, fourth, and fifth words of the Shema Yisrael. They are written upside-down so that they will correspond to their matching letter on the front of the mezuzah.
To “hack” this code you must decipher the letters using a method of substitution known as a one-shift “Caesar cipher,” meaning these letters are shifted one letter up from the letter they are meant to encrypt. (Reportedly, Julius Caesar used similar codes to encrypt his documents.)
This custom is not universal. Sephardic authorities do not allow any other writing anywhere on the mezuzah aside from the customary Divine Name Sha-dai. These authorities base their hesitation on Rambam’s sharp rejection of similar practices:
It is a common custom to write Sha-dai, on the outside of a mezuzah opposite the empty space left between the two passages. There is no difficulty in this, since [the addition is made] outside.
Those, however, who write the names of angels, other sacred names, verses, or forms, on the inside are among those who do not have a portion in the world to come. Not only do these fools nullify the mitzvah, but furthermore, they make from a great mitzvah — reflecting G-d’s unity and the love and service of Him, and the service of Him — a talisman for their own benefit. They, in their foolish conception, think that this will help them regarding the vanities of the world.
In a similar vein, Rambam writes elsewhere:
A person who whispers an incantation over a wound and then recites a verse from the Torah…., or who places a Torah scroll or tefillin over a baby so that it will sleep, is considered to be a soothsayer or one who casts spells. Furthermore, such people are included among those who deny the Torah, because they relate to the words of the Torah as if they are cures for the body, when, in fact, they are cures for the soul, as [Proverbs 3:22] states: “And they shall be life for your soul.”
Although Rambam would acknowledge the protective powers that comes in the merit of the mitzvah itself, he scorns those who portray the mezuzah as nothing more than a tool to achieve material aims.
Curiously, however, the insertion of these mysterious letters has been accepted in Ashkenazic practice from at least the eleventh century. The authorities justify this custom by pointing out that Rambam referred to those who made additions to the inside of the parchment, whereas these letters, like the Name Sha-dai, are specifically written on the backside to accentuate that they are not meant to be considered part of the mitzvah itself.
Even so, Ashkenazic custom disallows writing any of the other angelic names, codes, and runes mentioned by Rambam on either side of the parchment. Yet this was not always the case. Before Rambam’s view was accepted as normative halachah, symbolic runes and Biblical passages were often inserted in the margins of the parchment at strategic places in an effort to “supercharge” the protective power of the mezuzah. Many of these symbols are actually representations of letters from the ancient Paleo-Hebrew alphabet found in archaeological inscriptions and coins in Israel.
|R’ Chaim Naeh||R’ Moshe Feinstein||Chazon Ish|
|Tefach||3.2 in.||8 cm.||3.6 in.||9 cm||3.8 in.||9.6 cm.|
|Amah||18.9in||48 cm.||21.3 in.||54 cm.||22.7 in.||57.7 cm.|
|Four Amos||75.6 in.||1.9 m.||85.2 in.||2.2 m.||90.8 in.||2.31 m.|
|4 X 4 Amos||39.7 sq. ft.||3.7 sq. m.||50.4 sq. ft.||4.84 sq. m.||57.8 sq. ft.||5.4 sq. m.|
Throughout the book and the website, I will be using the Talmudic measurement terms tefach (handbreadth) and amah (cubit) or to their plural forms, tefachim and amot. Because there are several ways of calculating the conversion of Talmudic measurements into their contemporary equivalents, I have created this chart for easy reference.
Note: For practical purposes, these measurements have been rounded up slightly. For most halachic calculations, this would not pose a problem. However, if one is determining whether a room is big enough to require a mezuzah, these measurements might need to be adjusted downwards slightly.
In Israel, the opinions of R. Chaim Naeh and Chazon Ish are generally taken into consideration. R. Moshe Feinstein’s opinion is commonly followed in the United States.
Although the Chazon Ish’s measurements are larger, they are not necessarily stricter. It all depends on the context. For example, when one is trying to place a mezuzah within a tefach of the outside of the doorpost, he should be strict and utilize R. Chaim Naeh’s smaller measure.
According to Rambam, a doorway must meet the following ten conditions in order to require a mezuzah.
These conditions are useful as a checklist but can only provide general guidance. Although in practical halachah, not all Rambam’s definitions are followed unreservedly, they are all taken into consideration and, when they are not met, may create a doubtful obligation. Though we are careful to perform the mitzvah of mezuzah even in situations of doubtful obligation, in regard to the recital of a berachah, which entails the uttering of the Divine Name, we may only bless when we are sure that the berachah is necessary. Thus in doubtful placements, one should affix the mezuzah without making the berachah. Ideally, competent rabbinic guidance should be consulted in this matter as there are several exceptions to this general rule.
Alternatively, one who is affixing a mezuzah on a doorway that is clearly obligated, may make a berachah on it and have this placement in mind.
1. Minimum Area
The Torah instructs that we must put mezuzot on the doorposts of our “bayit.” Although in Modern Hebrew, bayis is generally translated as “house,” the Talmud writes that a bayit can even refer to a single room with a minimum area of four square amot.
Practical halachah deals with the mezuzah obligation of rooms whose area is formed by different combinations of width and length (e.g. two amot by four amot).
Rambam rules that a doorway only requires a mezuzah if it is framed by posts on both sides. In practice, we follow the authorities who requires a mezuzah even when a solitary post stands on the right side of a doorway.
The halachah deals with the dimensions and shape of these posts. In addition, it defines the exact placement of a mezuzah in archways and other unusual circumstances.
Practical halachah deals with lintels of unusual shape, position or purpose as well as doorways without a lintel, but whose ceiling edge can be seen as a lintel.A lintel (mashkof, in Hebrew) is the horizontal bar framing the top of the doorway. Rambam rules that without this very basic structural element, a doorway is incomplete and therefore exempt from mezuzah.
Rambam rules that a room without a ceiling is deficient, even if its doorways are otherwise complete. Practical halachah follows those authorities who obligate the gates and doorways of uncovered courtyards, patios, and porches in their own right, based on their opinion that the absence of a ceiling is integral to their design and their purpose.
According to Rambam, these spaces are only obligated when they open onto or lead towards a covered room.
Rambam rules that a doorway without a door is deficient and requires no mezuzah.
Practical halachah follows those authorities who require a mezuzah on such openings, in most cases.
6. Height and Width of Doorway
Rambam rules that a doorway must be of a minimal height of ten tefachim. Although Rambam does not mention a minimal width, the halachah follows those opinions who rule that it must be at least four tefachim wide.
The halachah deals with the correct placement of mezuzot on doorways of unusual height. The special halachic issues presented by curved archways are also explored.
7. Beit Haknesset & Beit Hamidrash
Rambam exempts these places precisely because they are dedicated to holy activities and not to normal dwelling. Indeed, the Talmud records that none of the gates and chambers of the Beit Hamikdash had mezuzot, except for those that served as living chambers.
Nowadays, the custom is to affix mezuzot on a Beit Hamidrash and even on a Beit Haknesset where people spend the day learning, as this is deemed “dwelling.”
8. Human Habitation
Rambam exempts storage rooms and barns from mezuzah. However, Shulchan Aruch rules that since humans use these structures, they are considered human habitats, unless other factors render them unfit.
9. Dignified Purpose
This is the source of the well-known halachah that a bathroom or a mikveh does not require a mezuzah.
10. Permanent Dwelling
Hotels, rentals, sukkot, trailers, ships and private jets are just a few of the many structures that do not qualify as permanent dwellings.
Placement Without Berachah
The following is a short list of situations that call for mezuzah placement without berachah. Other instances will be noted in the text:
- The doorway has no actual door
- The doorway does not have two posts on its sides.
- The doorway lacks a lintel
- Either the length or the width of a room is less than four amot.
Q: My little daughter loves to kiss the mezuzah before going to sleep. She keeps on asking me to move the mezuzah lower down on the post so she could reach it. I always tell her that it must stay where it is, but when she asks me, “Why?” I don’t know what to tell her except, “That’s the halachah!” To be honest, I would also love to know why!
A: The Talmud equates the mitzvah of tefillin to mezuzah that follows it in the first paragraph of the Shema. Just as Tefillin are placed on the upper part of the body and the head, so too, the mezuzah should be affixed within the top third of the doorway.
Also, the mezuzah must be visually noticeable to the adults who pass by it, as a reminder to observe the mitzvot incumbent upon them.
The custom of kissing a mezuzah, precious as it may be, cannot push aside these halachic principles. R. Yonason Rosenblum, in his classic biography of R. Yaakov Kaminetzky records:
Reb Yaakov was particularly attuned to the dangers of exposing children to any kind of falsehood. He once visited the kindergarten of his son Binyamin’s yeshiva and noticed that the mezuzah had been placed lower on the doorpost than halachically prescribed, so the children could reach it upon entering the classroom. The idea of getting children used to touching the mezuzah when they come into a room was a good one, said Reb Yaakov, but the means were wholly inappropriate. “Put the mezuzah on the upper third of the doorpost where it belongs,” he said, “and let them use a stool to reach it. Otherwise they will grow up thinking a mezuzah can be put anywhere you wish. One does not raise children with falsehood.”
Perhaps there is another lesson here as well: It’s important to convey to our children — and to ourselves — that our job is to lift ourselves up to meet our spiritual challenges, even when it’s “oh-so-tempting” to look for ways to simply lower the bar.
Q: I saw that the Kitzur writes that the mezuzah should be affixed at the beginning of the top third of the entrance. I’ve seen many homes where the mezuzah is within the top third, but not exactly at its beginning. Does the Kitzur mean to say that ideally one should use a tape measure to determine the exact spot where the top third begins?
A: The Kitzur’s ruling reflects the consensus of contemporary poskim that one should ideally measure the doorway in order to affix the mezuzah precisely at the beginning of the top third. Care should be taken to lift it slightly from the exact line, so that no part of the mezuzah is lower than the top third.
However, you have correctly observed that the general custom follows those authorities who deem anywhere within top third as equally acceptable. Indeed, several authorities hold that its ideal position is higher up on the post, preferably at about shoulder height. Care should be taken that it is not place in the top tefach of the doorpost.
The Torah commands us to place a mezuzah on the right doorpost as we enter a room or a gate. Even if all the dwellers in the home are left-dominant, the mezuzah is placed on what would be called the “right” for most people.
This requirement generally poses no problem when affixing the mezuzah to the main entrance of the house. However, determining the proper placement of mezuzot on interior rooms which are accessible from several entrances can be quite daunting.
Whenever possible, a rabbi should make these determinations as there are many factors that must be considered, and a mezuzah placed in error on a left doorpost is invalid. In most cases, a misplaced mezuzah must be transferred to the correct post and a new berachah recited. However, if a rabbi does not say that the present position is incorrect, but rather suggests that it is preferable halachically to move it to the other post, a new berachah is not necessary.
סעיף ד שְׁנֵי בָתִּים אֲשֶׁר לְכָל אֶחָד יֵשׁ פֶּתַח לִרְשׁוּת הָרַבִּים אוֹ לֶחָצֵר, וּבַמְּחִיצָה אֲשֶׁר בֵּינֵיהֶם יֵשׁ גַּם לְכָל אֶחָד פֶּתַח לִרְשׁוּת הָרַבִּים אוֹ לֶחָצֵר, וּבַמְּחִיצָה אֲשֶׁר בֵּינֵיהֶם יֵשׁ גַּם כֵּן פֶּתַח, וְהַשְּׁתָּא יֵּשׁ לְהִסְתַּפֵּק בְּפֶתַח זֶה בְּאֵיזֶה צַד יִתֵּן אֶת הַמְּזוּזָה אָזְלֵינַן בָּזֶה בָּתַר הֶכֵּר צִיר. פֵּרוּשׁ, בִּמְקוֹם שֶׁנַּעֲשִׂים הַצִּירִים לְהַדֶּלֶת שֶׁהַדֶּלֶת נִפְתַּחַת לְתוֹכוֹ, זֶהוּ עִקַּר הַבָּיִת, וְנוֹתְנִים אֶת הַמְּזוּזָה בְּצַד הַיָּמִין שֶׁנִּכְנָסִים לְתוֹכוֹ. וְדַוְקָא כְּשֶׁשְּׁנֵי הַבָּתִּים שָׁוִים בְּתַשְׁמִישָׁם. אֲבָל אִם אֶחָד הוּא עִקַּר תַּשְׁמִישׁוֹ, בָּזֶה לֹא אָזְלֵינַן בָּתַר הֶכֵּר צִיר, אֶלָּא לְעוֹלָם נוֹתְנִין אֶת הַמְּזוּזָה בְּצַד הַיָּמִין שֶׁנִּכְנָסִים לְהַבַּיִת אֲשֶׁר עִקַּר תַּשְׁמִישׁוֹ שָׁם, אֲפִלּוּ הַדֶּלֶת נִפְתַּחַת לְתוֹךְ הַשֵּׁנִי
Kitzur 4. When there are two rooms, each room with a doorway opening onto a street or a courtyard, and in the wall between the rooms there is also a doorway, the proper mezuzah placement on the doorway between the two rooms is unclear. The determining factor in this regard is the “indication from the hinge,” that is: the side where the hinges are attached and towards which the door opens. This is considered the primary room, and we affix the mezuzah on the right side of one who enters that room.
The above applies only when the two rooms are used equally. However, if one of the rooms is more actively used, in that case, we are not guided by the “indication from the hinge.” Rather, the mezuzah must be affixed on the right as one enters the room more actively used, even if the door opens into the other room.
Determining Right-Hand Placement in Doubtful Situations
The details of this important halachic determination are many, and preferably a rabbi should be consulted in cases of doubt. Nevertheless, the following order of priorities can be followed as a general guideline.
- Priority 1 – Internal
- Priority 2 – Main entrance
- Priority 3 – Main room
- Priority 4 – Indication from hinge
Priority One — Internal
If a room has only one entrance, it is obvious that the mezuzah is placed on the right side of one going into that room.
This is true even if the door of the room is hinged so that it opens into the external room. The direction of the door’s swing is not enough of an indication to negate the fact that the doorway is an entrance to the inner room.
This is also true even if the inner room is used much less than the outer room. For example, if a formal dining room, used on rare occasions, is accessed only by walking through a busy family room, the mezuzah is nonetheless placed on the right of one going into the dining room.
Priority Two — Main Entrance
Often rooms can be accessed from more than one door, and therefore one of them cannot be defined as internal to the other. The doorway between two such rooms can be looked at as both an entrance and an exit from the one to the other. In these cases, one assesses the direction that people primarily take when going from one room to the other and places the mezuzah on the right of one going in that direction.
For example, a bedroom may have a second door from the garden, which is used from time to time. Coming from the garden, the main bedroom door is then also an entrance into a hall as much as it is an entrance into the bedroom. Nevertheless, since one generally enters from the hall into the bedroom from its main door, the mezuzah is placed on the right post of that entrance, going in.
Priority Three — Main Room
When none of the rooms is more internal than the other, and the primary direction of traffic between them is equal, we then look at the quantity of time spent in each of the rooms. The room one occupies the most is then called the “main” room, and the less used room is thought to lead into it. One places the mezuzah on the right side of the entrance to the “main” room.
For example, mezuzot are placed on the right of corridor doors which lead into the rooms that they service. This is true even if those rooms are not considered more internal than the corridor as they can be accessed from another door. It is also true even if the doors swing into the corridor.
Priority Four — Indication from the Hinge
In Talmudic times, doors were not set into the doorways but rather hinged on the inside of the room, so they could not be tampered with from the outside. As such, the position of the hinge was a clear indication of which room was considered internal. Nowadays, we assume that the swing of the door into one area indicates the direction of entry.
In the Absence of a Clear Indication
If both rooms are accessible from the front door, equally trafficked, equally used, and there is no indication from the hinge (e.g. the doorway leading between them has no door), both doorposts can be considered right doorposts of an entrance, and one can place the mezuzah on either one.
There are several holy customs that reinforce the principles quoted here by the Kitzur. Rema cites the opinion of Maharil that as one leaves or enters his home, he should put his hand on the mezuzah case and recite:
ה’ ישמר צאתי ובואי מעתה ועד עולם
May Hashem guard my going out and my coming in from now and forever. 
However, these early sources mention only the placing of the hand on the mezuzah. Chayei Adam and Kitzur Shulchan Aruch mention “kissing” the mezuzah, but they may only be referring to the loving placement of the hand.
Many have the custom to kiss their hand after touching the mezuzah. This custom is first mentioned by the kabbalist R. Chaim Vital. He writes, in the name of Ari-zal, that when leaving one’s home, one should place his middle finger over the name Sha-ai inscribed on the back of the mezuzah. He then should kiss his finger and pray to Hashem to save him from the yetzer ha-ra — evil inclination. (Yetzer in Hebrew is spelled יוד צדי ריש . The hidden ending letters, ש-ד-י spell Sha-dai.) 
Many have a custom to touch every mezuzah they encounter, though only the mezuzah of the outer doorway is mentioned in the halachic sources.
Some have the custom of touching the mezuzah before going to sleep.
The Maharil records a special formula which should be recited upon leaving the home for a trip outside the city:
“בשמך טל אטלה”
“In Your Name, I shall surely be protected.”
The gematria (numerical value) of טל (thirty-nine) is equal to that of the formula כוזו which is inscribed on the back of the mezuzah. Each of these four letters are one letter up from the four-letter ineffable name of Hashem.
 Menachos 44a. The Talmud states that he who does not place a mezuzah on his door transgresses two commandments. But see Rambam, Sefer Hamitzvot, Shoresh 9, who explains that though mitzvot are repeated for emphasis, they are considered as one in the 613 count.
 Teshuvos R. Akiva Eiger 1:66; Avnei Nezer Y.D. 380. This may have implications in several halachic considerations, as we shall explore.
 Shulchan Aruch Y.D. 286:16-17.
 Shulchan Aruch Y.D. 271
 Keses Hasofer 2:12
 Yerushalmi Megillah 1:9.
 Rema Y.D. 271:6, citing Zohar, Terumah 72a.
 Nir-El, Yoram; Broshi, Magen (2009). “The Black Ink of the Qumran Scrolls”. Dead Sea Discoveries. Brill. 3 (2): 157–167. JSTOR 4201558.
 Shulchan Aruch O.C. 32:3.
 Shabbos 23a
 Eruvin 13a.
 Keses Hasofer 2:12; Aruch HaShulchan 271:34; Birkei Yosef Y.D. 271:7.
 Shabbos 28b, Teshuvos Dvar Shmuel 162.
 Taanis 20a.
 Rema Y.D. 271:7; Bei’ur HaGra 271:23.
 Turei Zahav 271:7; Shach 271:13; Keses Hasofer 3:16.
 Pitchei Teshuvah Y.D. 271:21, citing Dvar Shmuel 164.
 Shevet HaLevi 2:136, citing Ramban, Yisro.
 Keses Hasofer 3:16, and Bnei Yonah op. cit. n. 7.
 Shabbos 104a; Yerushalmi Megillah 1:1.
 Sanhedrin 21-22.
 Shulchan Aruch O.C. 36.
 Shu”t HaRosh 3:11; Tur Y.D. 274.
 Yabia Omer Y.D. 2:20; Halichos Shlomo 4, note 31.
 Shevet HaLevi 10:7:2.
 Chazon Ish O.C. 9:6
 Zohar, Va’etchanan 266, cited in Beit Yosef 288:14.
 Ramban, Bereishis17:12
 Kad HaKemach, Erech Mezuzah.
 Hilchos Sefer Torah 5:4.
 R. Moshe Alshich, Toras Moshe, Parashas Va’eschanan.
 Rambam, Hilchos Sefer Torah U’Mezuzah 5:4
 Rambam, Hilchos Avodas Kochavim 11:12.
 Rashi, Sefer HaPardes, Seder Mezuzah; Machzor Vitri, p. 648; Yerei’im “Taf”.
 Shulchan Aruch Y.D. 288:15.
 Rashi and Ran, Sanhedrin 21b.
 Rambam, Hilchos Sefer Torah 6.
 In contrast, a renter may only be obligated rabbinically according to many authorities. See Agur B’ohalecha 2:75, who writes that because of the greatness of this mitzvah, even in doubtful rabbinic obligation it is praiseworthy to be strict.
 This halachic principle is called “safeik berachot l’hakel” (we are lenient regarding doubtful berachot).
 For example, if there are several compounded doubts regarding an obligation. These complex considerations can only be assessed by a halachic authority.
 Aruch HaShulchan Y.D. 286:3; Sukkah 3a.
 Shach Y.D. 287:1; Biur HaGra Y.D. 287:1.
 Rosh, Hilchos Mezuzah 11.
 Rambam, Hilchos Sefer Torah 6:8.
 Hagahos Raavad, op. cit.; Shulchan Aruch Y.D. 286:15; Chayei Adam 15:9; Mezuzot Beitecha (Sha’ar HaTziun 121) advises that one should endeavor to make a berachah on another mezuzah and have this one in mind, as most Rishonim dispute the Rambam’s position.
 Shach Y.D. 287:2. Aruch HaShulchan rules that if the opening is wider than 3 tefachim a mezuzah should be affixed without a berachah.
 Rambam, Hilchos Sefer Torah 6:6.
 Yoma 10a.
 Mezuzot Beitecha 286:89; Agur B’ohalecha 33:1.
 Shulchan Aruch Y.D. 286:2.
 Shulchan Aruch Y.D. 286:4.
 See chart. 2.31 m / 90.8 inches according to Chazon Ish.
 Agur B’ohalecha 12:9:26, citing Minchas Pitim.
 See Yitzchak Yikarei 6:9:24, citing R. Shlomo Zalman Auerbach.
 R. Yonason Rosenblum, Reb Yaakov (Artscroll Pub., pp. 326-7).
 Shulchan Aruch 289:2; Mezuzot Beitecha 289:2, Sha’ar Hatziun 23; Beit Baruch 7:23; Agur B’ohalecha 12:2; Teshuvos V’Hanhagos 2:538.
 Nekudos Hakesef Y.D. 289:2; Bei’ur HaGra 289:7.
 Nekudos Hakesef Y.D. 289:2.
 4’ 6” (1.4 meters).
 Yoma 12b.
 Rema Y.D. 289:2; Shach 289:5.
 Shulchan Aruch Y.D. 289:2.
 Beit Yosef Y.D. 289; Bei’ur HaGra Y.D. 289:9.
 Chayei Adam 15:8; Kitzur Shulchan Aruch 11:4. Cf. Agur B’ohalecha 27:14, who opines that most authorities hold that the indication from the hinge takes precedent over the main room factor.
 Priority 4.
 Priority 3.
 This is determined by the first entry through the doorway and not be the subsequent re-entry into the original room.
 Da’as Kedoshim 289:11; Igros Moshe Y.D. 1:176; Chovas HaDar 8:4; Agur B’ohalecha 27:13. The language of Kitzur Shulchan Aruch here is ambiguous regarding the criteria of “main entrance.”
 Chayei Adam 15:18; Agur B’ohalecha 27:25; Sha’arei HaMezuzah 13:17. Cf. Da’as Kedoshim 289:12, who asserts that one considers the qualitative importance of the activities, e.g. sleeping vs. eating.
 Priority One.
 Priority Two.
 Chayei Adam 15:18; Agur B’ohalecha 27:25.
 Shevet HaLevi 2:152; Agur B’ohalecha 27:36. One should not recite a berachah on this placement. Cf. Igros Moshe Y.D. 1:176, who exempts this doorway completely.
 Rema (Y.D. 285:2) adds ‘and enters’, though this is not mentioned by Maharil. Both Chayei Adam and Kitzur Shulchan Aruch only mention the custom upon leaving. However, Kuntres HaMezuzah (285:29) lists several Acharonim who follow the Rema.
 Rema )op. cit.) cites this verse from a Midrash. According to Kitzur Shulchan Aruch the full formula is
‘ה’ שומרי ה’ צלי על יד ימיני ה’ ישמר צאתי ובואי מעתה ועד עולם’ , which also incorporates the verse cited by Maharil. Darchei Moshe (Y.D. 285) writes that this custom developed from the story of Onkelos, who placed his hand on a mezuzah and cited this verse. Kuntres HaMezuzah asserts that Rema consciously did not cite this custom as an obligation, as it has no explicit source in the Talmud. Indeed the students of Terumas Hadeshen reported that he looked at the mezuzah but did not touch it unless he was going on a journey.
 Cited by Birkei Yosef Y.D. 285:2.
 Perhaps this can be explained by the requirement to constantly check the correct placement of all mezuzot, mentioned by Chayei Adam (15:1).
 Chovas HaDar 1.
 Though cited by Darchei Moshe, Shach and Aruch HaShulchan, this custom is omitted by Rema, Kitzur Shulchan Aruch and Chayei Adam. However, Kuntres HaMezuzah states that even those who do not have a custom to recite verses daily as they leave the house, should recite this as a prayer for safety on the road. He cites Yam Shel Shlomo (Yevamos 1:3) who recommends reciting it three times.
 י-כ, ה-ו, ו-ז, ה-ו.