i didn't size up. got a medium, which based on the measurements should fit (and it does fit well tbh). if i had sized up, the neck opening would have been way too big.here are a couple fit pics just to show how big the neck opening is. it's not enormous, but it's definitely wider than a normal crew. (sorry the pics aren't too great, it was hard to just take pics of the neck based on the mirrors in my apartment and my phone camera). hope this helps.