Hi ET,
The sizes are just s/m/l, and are obviously geared around some very skinny triathletes. I had to buy a large, and I don't consider myself that huge, (my "normal" size yoyos between 12 & 14 depending on diet, exercise, time of the month, cut of clothes, etc). I did try a medium, but couldn't get it over my hips, so gave up trying to pretend.
I hope that helps, Jane