Measure the widest part of your dominant arm. Do not flex when taking this measurement
Measure straight around the back, over the widest part of your stomach. Leave room to snuggly fit 2 fingers in between the tape and your stomach. Stand naturally, without sucking in or puffing out your stomach.
This measurement should be taken just under the arms, closely around the body
With both arms down by your side, measurement taken from the tip of the left shoulder point, along the top of the shoulder just below the base of the collar, to the tip of the right shoulder.