From the package:
Size S, 6-8, 21 = 23" waist
Size M, 10-12 = 23-26" waist
Size L, 14-16 = 26-28" waist
Size XL, 18-20 = 28-30" waist

I didn't know what size to order, as no sizing info is given.  Luckily I ordered the L for  my 13-year old.  They're a bit large, but he'll grow into them.

Good Hanes quality.  Nice colors for boy teens.  Comfy. Should last awhile.