All measurements are in inches, from armpit to armpit, multiply by two for approximate chest size
Girly shirts:
XXL - 19
XL - 18
L - 17
M - 15.5
S - 13.25
Regular shirts:
XXXL - 28
XXL - 25
XL - 24
L - 20.5
M - (didn't have one handy)
S - 18
As you can see, the sizing is VASTLY different between the shirt styles.
