Question:
Is there a minimum required width for the shoulder area of a tallis katan, and does this requirement apply according to all opinions?
Answer:
According to Admur in the Shulchan Aruch, the shoulder area is included in the measurement of the tallis katan, and therefore it should have a noticeable width. Thus, one should be careful that the shoulder area of the tallis katan is not made too narrow. Practically, many Poskim write that each shoulder should be at least 7.2 cm (approximately 3 inches) wide. Others are more stringent and recommend that each shoulder area be approximately 21 cm wide. However, some authorities point out that according to Admur in the Siddur who rules that the shoulder area is not included in the measurement of the tallis katan, accordingly, there is no minimum width requirement for the shoulders, and even a narrow connection is sufficient, provided it connects the front and back panels of the garment.
Thus, while it is proper to make the shoulders reasonably wide, there is room to be lenient regarding the minimum width according to the ruling of Admur in the Siddur.
Sources:
Admur 16:2; Magen Avraham 16; Maharil, Hilchos Tzitzis 4:4; Mateh Moshe 9; Mishnah Berurah 16:4; Ashel Avraham 16; Kaf HaChaim 16:6; Chazon Ish, Igros 10; Ketzos HaShulchan, Hosafos p. 86; Piskei Teshuvos 16:2 footnote 16.