The Size of Tefillin
Question: Is there a minimum size for the battim of the tefillin?
Discussion: Shulchan Aruch43 states that battim can be any size. However, Mishnah Berurah44 cites a number of Acharonim who say that battim which measure one square thumb breadth (2x2 cm according to R’ Chaim Naeh, or 2.4x2.4 cm according to Chazon Ish),45 or less, are actually invalid. Furthermore, Mishnah Berurah46 also cites the view of the Geonim, who say that lechatchilah, battim should measure at least two square thumb breadths (4x4 cm according to R’ Chaim Naeh, and 4.8x4.8 cm according to Chazon Ish). Although Shimusha Rabba (which is the source of the Geonim’s view) actually discusses the size of a shel rosh, Mishnah Berurah cites their view without differentiating between shel yad and shel rosh, and both Bach47 and Ba’er Heitev48 write explicitly that also the tefillin shel yad should ideally be the size of two square thumb-breadths.
In summary, both the shel yad and the shel rosh should ideally measure at least two square thumb breadths. If they measure one square thumb breadth or less, they might actually be invalid.
In practical terms, standard contemporary tefillin measure
5x5 cm and, therefore, qualify as being large enough according to all views.
Question: Why do some people have a smaller tefillin shel yad than tefillin shel rosh?
Discussion: There is discussion amongst Rishonim and Acharonim regarding the correct placement of the tefillin shel yad. Both Shulchan Aruch and Rema rule that the correct placement is on the muscle, on the lower half of the bone which extends from the shoulder until the elbow (illustration 1).49 However, Vilna Gaon disagrees,50 and says that the tefillin may be placed anywhere on the muscle, whether on the upper or the lower half. Ideally, one should follow the ruling of Shulchan Aruch and Rema.51
Now, it can sometimes be difficult (particularly for bar-mitzvah boys and for older people) to fit a standard sized shel yad (i.e., a shel yad measuring 5x5 cm) into the area designated by Shulchan Aruch and Rema. However, a shel yad which measures 4x4 cm (so that it reaches the ideal size of two square thumb breadths, at least according to R’ Chaim Naeh), will fit into the prescribed area far more easily. Therefore, some people wear a standard sized shel rosh, along with a shel yad which is somewhat smaller than standard.
Question: Since the requirement for tefillin to measure two square thumb breadths is simply lechatchilah, whereas the requirement to place tefillin in the correct area could be considered necessary even bedeived, it would seem that somebody who has difficulty positioning standard-sized tefillin in the area prescribed by Shulchan Aruch and Rema should, indeed, make a point of wearing a shel yad which is smaller than standard. Is this correct?
Discussion: As we have already mentioned, although Shulchan Aruch and Rema say that the shel yad must be placed on the lower-half of the muscle, Vilna Gaon disagrees and says that it may be placed anywhere on the muscle. Vilna Gaon’s opinion has a firm basis in Gemara and seems to be supported by the vast majority of Rishonim. As a result, a number of Poskim imply that the essential halachah follows Vilna Gaon’s opinion.52
Therefore, some contemporary Poskim write that since the ideal size for a shel-yad is 5x5 cm, and one fulfills the mitzvah according to Vilna Gaon as long as the bayis rests anywhere on the muscle, it is preferable not to change from the standard-sized tefillin.53
However, others say that since a shel yad which measures
4x4 cm does reach the size of two square thumb breadths (at least according to R’ Chaim Naeh), and the entire requirement for tefillin to measure two thumb breadths is simply lechatchilah, it is indeed preferable to wear a shel yad which is somewhat smaller than standard, if one must do so in order to fit the tefillin into the area prescribed by Shulchan Aruch and Rema.54
43 32:41.
44 Ibid., note 189. See further discussion of the various views in Tefilla LeMoshe, Vol 1 pp. 207-219.
45 See Chazon Ish, Orach Chaim 39, and Middos V’Shiurei Torah (pg. 89).
46 Ibid.
47 Ibid. 27.
48 Ibid. 60.
49 Rema 27:1, Shulchan Aruch ibid. 7.
50 Beiur HaGra to 27:1, cited in Mishnah Berurah ibid. 4.
51 Mishnah Berurah 27:4.
52 See Mishnah Berurah 27, note 4, and Aruch Hashulchan ibid. 4. [See also Vayashav Hayam 2:4, who attempts to prove that the position of Shulchan Aruch is actually like Vilna Gaon, and in fact Rema is the only opinion who holds this way. He further states that even Rema only means lechatchilah, whereas bedieved there is no problem if the tefillin rests even on the upper half of the muscle. The vast majority of Poskim, however, do not understand Shulchan Aruch’s view this way (see Mishnah Berurah ibid.)].
53 Da’as Notah 3:241; see also Halichos Shlomo, Tefillah 4:27; Shevet Halevi IX: 220:2; Vedibarta Bam II:3.
54 Zichron Eliyahu 10, Sikum Hahalchos 2; Tefillah LeMoshe 4:7.