I measure my chest relaxed and then with the lats expanded and chest flexed. I have someone run the tape underneath my armpits and the tape goes at the highest part of my chest, which is as high as the armpit will allow without making the tape crooked. I find it impossible to take the measurement myself. I dont think anyone does it the same anyway.So the best way to gauge your personal progress is to measure the same way each time IMO. Hope that helps