Youth Sizes:

S - 6/8 = 36" Chest/Body Width
M - 10/12 = 38" Chest/Body Width
L - 14/16 = 41" Chest/Body Width
XL - 18/20 = 44" Chest/Body Width

Adult Unisex Sizes:

XS = 43"-44" Chest/Body Width
S = 45"-46" Chest/Body Width
M = 47"-48" Chest/Body Width
L = 49"-50" Chest/Body Width
XL = 53"-54" Chest/Body Width
XXL = 57"-58" Chest/Body Width
XXXL = 61"-62" Chest/Body Width