The shirts are designed to compress so you should order the size closest to your natural measurement.

MEN
MEN chest S M L XL
CM 84 92 100 108
INCH 30 32 6/7 35 5/7 38 4/7

WOMEN
WOMEN chest S M L XL
CM 85 91 97 103
INCH 30 5/14 32 1/2 34 9/14 36 11/14