halacha - Is there a minimum size that a Tallis Kattan has to be?

Is there a minimum size that a Tallis Kattan has to be in order to be Yotzei the Mitzva of Tzitzis according to all Poskim? If there is a minimum size, what is it?

Answer

The main shiur is that which will cover the head and most of the body of a child who can walk independently in the marketplace (menachos 41). The Tur gives an age of 9.

There is a dispute about the second condition of the braisa that an adult would wear it in the street occasionaly. The Tur holds this is a second precondition and so the Rema adds this even though the mechaber doesn't ((O.C. 16:1- see magen Avraham). The 2nd precondition alone would not be enough of a shiur. However, the Mishna Berura (16:2) says that it seems from the Bach that if an adult (13 y/o) would wear it on a regular basis, you wouldn't need the precondition of the child.

BOTTOM LINE: The Mishna Brura (ibid.) quotes a shiur of 3/4 Amah L x 1/2 Amah W, but then quotes the Artzos haChayim who say this shiur has no basis and says that "Anshei maase" are particular to have an Amah on each side, but you should have at least 3/4 of an Amah, since the "Mesamchei Lev" measured a 9 y/o and found him to be 1.5 Amos.