The halacha, as set forth by the Mishna Berurah (27:4), requires the Shel Yad to be above the area where the bicep begins to become elevated. I've read that there is a dispute regarding whether the elevated part of the bicep is determined when to arm is outstretched, or when the arm is at a 90-degree angle. Does anyone have a source for one (or both) sides of this dispute?

  • 2
    Others will remember the sources for the discussion of the tall thin tefillin that were in style a couple of decades ago, as a way of being able to make them fit on the muscle even when the arm is bent. However, that seems to be a strong piece of evidence that the real halacha is, the muscle when the arm is outstretched: because no one ever heard of the issue till then, and people have been wearing large tefillin for centuries with no one complaining.
    – MichoelR
    Jan 17, 2021 at 16:09
  • @MichoelR R Yosef Karo's tefillin was tall and narrow. In early days people used to wear much smaller tefillin than is popular today.
    – Double AA
    Jan 17, 2021 at 16:20
  • Yeah, sure. But if I remember right, I saw the גר"ז and the ערה"ש both suggest that a lot of problems would be avoided with bigger tefillin. Certainly Chabad has been using big tefillin for a long time. Using small tefillin is not evidence (unless they say that's why), using big tefillin is. Especially because it seems that there is actually room for two tefillos of the hand where we put just one.
    – MichoelR
    Jan 17, 2021 at 16:25
  • Ben Ish Chai and the Taz talk about wearing Rashi and R"T at the same time, one above the other...
    – MichoelR
    Jan 17, 2021 at 16:27
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    @Mich Exactly. Two is crowded. Three or two modern size ones, not a chance. Even one modern Chabad bayit is a stretch
    – Double AA
    Jan 17, 2021 at 17:35

2 Answers 2


Quote for https://www.hasofer.com/html/tefillinposition.html:

Lowest point for tefillin begins where the biceps muscle starts to elevate and is normally bulged. The tefillin must never pass below this point! {Mishna Berura 27:4} With your arm outstretched (according to the ruling of Harav Hagaon Rabbi Y. S. Elyashiv, shlita) as in the above diagram, you should carefully check your arm to recognize exactly where your biceps muscle starts to bulge, and always make sure the tefillin are positioned slightly higher than this point so that they will remain in the correct placement area even if they slip down a little.


Trying to turn a discussion in comments into an answer:

  1. The Shulchan Aruch and the Rema (27(1)) poskin like the opinion that the arm tefillah should be put on the half of the muscle toward the elbow. (The Gr"a points out that every other Rishon argues and allows the entire muscle. And the Aruch Hashulchan there actually holds that the entire upper arm is kosher.) But the minhag is like the Shulchan Aruch: on the bottom half of that muscle.
  2. Orach Chaim 32(41), starting with the Tur:
    The Bach in OH 32 (also Keset Hasofer, Ch. 21) says that both the hand and the arm tefillin should lechatchilah be at least two etzbaos (fingerbreadths) (that includes the תיתורא base section surrounding the בתים), according to the שימושא רבה. Others argue (see the Shulchan Aruch Harav there) and say that the שימושא רבה was only discussing the head tefillah; the arm one can be smaller, down to one etzba.
  3. The conclusion of the gemara in Eiruvin 95b is that the arm has room for two tefillos.
  4. Various recent poskim (see there the Shulchan Aruch Harav, Aruch Hashulchan, Keset Hasofer and especially the Mishnah Berurah) caution against tefillin that are too small; they say that it is very likely that the result will be parshiyos that are badly written and actually posul. However, the Mishnah Berurah also cautions against tefillin that are too big, that is, larger than 4 etzbaos, saying that they will likely not fit in the required area and the person will not fulfill his obligation.
  5. Some communities (Chabad) use large tefillin, and pretty much everyone today that I see uses ones that are well bigger than two etzbaos (always meaning, including the תיתורא).

Okay! I am of average dimensions, 5'10'', and I measured my arm. Bent, 10 cm from elbow to end of muscle. Half of that is 5 cm = way less than four etzbaos = not nearly enough room for two tefillos. Straight, 15 cm / 2 = 7.5 cm, more-or-less enough room for two tefillos of two etzbaos each, or one big one of four.
So I ask you. How is that no one (that I saw) from around the time of the Mishnah Berurah even discussed the fact that for normal people a tefillah shel yad of four etzbaos is way too big to wear? It's certainly too big for me. Chabad has apparently been using them for a long time, and never noticed a problem. We are all strict to put them on the bottom half of the muscle, we all have pretty big tefillin these days, and until twenty years ago no one noticed that they don't fit!
The easiest conclusion is that the muscle is measured with the arm extended, in which case I would have enough room for one tefillah of 4 or two of 2, and so would most others.

There may be other solutions. Since the present situation is a combination of chumros, perhaps all poskim happened to hold in ways, different ways, that avoid the issue. The Gr"a and most Rishonim may just have put the tefillah in the middle of the muscle. Pretty much everyone else may have used smaller tefillin till recently and held that the hand tefillin isn't two etzbaos. If so, maybe only Chabad need hold that the muscle is measured extended. The rest of us might be stuck, trapped between several chumros with no way to wear our large tefillin.
It would still be surprising that no one discussed the issue. [Of course, I may just be ignorant of those who did.]

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