XXL - 22" PTP
*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.
Small - 16" PTP
Medium - 17" PTP
Large - 18" PTP
XL - 19" PTP
These are classed as 'Armani Underwear' so come very tight fitting. Depending on how you want the fit, id recommend at least a size up, possibly two!