Measure the distance from armpit to armpit, double it and this is the measurement you should use below.

Mens Size Guide

Small - 36" chest

Medium - 38/40" chest

Large - 42/44" chest

XL - 48" chest

XXL - 50 - 52" Chest (note very large)

Ladies Size Guide

Small - (8-10) is to fit 32/34” chest (81/86cm)

Medium - (12-14) is to fit 34/37” chest (86/94cm)

Large - (14 -16) is to fit 37/40” chest (94/101cm)

Kids Size Guide

Kids 2-3yr
3-4yr
5-6yr
7-8yr
9-11yr
12-13yr