XS- Designed for women with a size 32 pants and no more than a 75 chest size.
S- Designed for women with a 34-36 pants size and no more than an 85 chest size.
M- Designed for women with a 32-38 pants size and no more than a 90 chest size.
L- Designed for women with a chest size of 90 and up.
The model in this photo is wearing a size S.