Wrestlers! Help me size a singlet!

Halloween is fast approaching and one of my costumes for the year is a professional wrestler (and a cow-orker is going to be my sexy manager). I need a singlet and can’t seem to find one at a store in town, so off we go to the internet. I’ve never bought a singlet and the sites I’ve been to don’t seem to have any kind of sizing charts and of course I won’t be able to try them on. I guess the first-time buyer is just supposed to know instinctively what size to get. Anyway, little help here y’all? What is a good way of converting singlet to understandable measurement?