When each of my sons came of age (actually I still have one son well under bar mitzvah age), it was usually a bit of a challenge to explain to them what size tallit katan they should wear, because the minimum size for a garment to require tzitzit is very big on your typical bar mitzvah boy. Of course some of my boys were more receptive, some less.

Today I received an inquiry from a prospective customer asking about tzitzit sizing for his sons.

I'm looking to place an order for myself and my twin boys. I'm interested in getting wool tzitzit.

I'm 6'1" and typically wear a XL shirt size. Can you advise which size tzitzit I should buy that will fit me?

For my twins this will be for their Bar Mitzvah so this will be for a 13-year-old, and they are average size.

     Thank you, Jeremy

I explained to Jeremy that according to halacha, there is a minimum size requirement for any tzitzit garment (shiur beged). This is a very complicated topic, and I'm not qualified to make any authoritative recommendations.

From a practical standpoint, it's somewhat problematic because the smallest halachic sizes are typically quite big on a bar mitzvah boy. So a father has to know what size the boy should be wearing, and he needs to know his son, so that he has a feel for how much he can coax him into wearing a big tzitzit garment and tucking in a lot. So if you ask a rabbi what the minimum size is, you might want to ask him for guidance in how to present that to a bar mitzvah boy.

According to some opinions, the minimum size is what the Grach Na'eh holds: a Size 5 / US Size 20 in wool (which is equivalent to a Size 8 / US Size 20 in cotton). Certain rabbis may be of the opinion that it's okay to go down a size. And there are poskim, notably Rabbi Moshe Feinstein and the Chazon Ish zt"l, who hold you need to go up to a Size 22 or Size 24.