I am a 38, I ordered a large based on sizing chart and they felt comfortable at the waist but kinda loose everywhere else. The gimmick "sack" was less effective than hoped for, unless I wore my underwear up to my navel. IF I were to buy them again, I would go a size smaller, but I will likely stick to my CK's. I personally didn't feel the benefit of the sack but I think that had a lot to do with the cut. The material was very comfortable and I WILL continue to wear them, but I may just have to roll the elastic once to get the proper fit.