Small - 21" PTP
Medium - 22" PTP
Large - 23" PTP
XL - 24" PTP
XXL - 25" PTP
XXXL - 26" PTP
Allow for padding with these measurements. I would recommend going true to size!
*PTP is the measurement from one arm pit to the other.
If unsure on the fit, compare measurements to another item you have that fits.