I am usually a small in underwear, but have been consistently working out and the band of my underwear was starting to be too tight. I ordered 3 pairs of these and figured small/mediumn was going to be good, based on only having a bit too much tightness on very small make of current underwear. And also, I looked at the size good. I have 40" hips and 27" waist. So this seemed to indicate I was within the medium size. Well, the band is too tight on all of them and I'm stuck with them, so that sucks. I also got the luna thong since isince it made more sense to get it on sale instead of paying shipping, and I got a m/L in that one, it fits perfect. So PSA for anyone with similar measurements.