(Ed: From the comments of the Mishnah Berura to this siman, we see that in his day, there was a problem with people buying and wearing talis katan’s that were too ‘katan’, i.e. smaller than halachic “code”. Sometimes the garment itself was too small, and sometimes they would even take two panels – front and back - and connect them with nothing more than shoulder straps! The Mishnah Berura was writing to encourage people to follow halachic specification and to caution them not to make brachos over these garments! Baruch Hashem, today, ready-made mitzvah objects abound, adherent to the highest standards and crafted with amazing beauty and workmanship. We must thank Hashem for blessing us with the opportunity to fulfill mitzvos with such bounty. We also owe it to Him to be knowledgeable on how to perform the mitzvos properly.)
Answer: According to the Shulchan Aruch, a garment - to be considered large enough for the mitzvah – must cover the torso of a nine-year-old boy. The Rama adds that the garment, although made for a child, must be such that even a 13-year-old would not be embarrassed to walk outside wearing it on occasion! OK, so how large is that, in real terms? The Mishnah Berura concludes that it should preferably be an entire ‘amah’ wide and long in both front and back, and certainly no less than ľ amah. (Ed: An amah is 6 tefachim. Rabbinic opinions for the conversion from tefachim to inches range from 3-4 inches per tefach. For ‘mitzvos mid-oraisa’ – Torah mitzvos – we assume the more stringent opinion. Thus we are looking at a range of somewhere between 18-24 inches.)
Why do some talis-katan’s have a V-neck? Because some authorities maintain that we must measure the length starting from the bottom of the neck-hole! Having a V-neck means that there is full material all the way up to the neck on both the front and back, so that one can begin measuring the length from the top! Get it?
One more thing: It is common for the material of the talis katan to scrunch up and curl so that its size seems to be diminished. (Ed: Has that every happened to you?) That’s no problem – it still counts as its full-size! [Ed: Please refer back to your notes on Siman 9 for a discussion on the difference between woolen and cotton ‘begadim’ (garments).]