To measure for your belt wrap a measuring tape (or string if you don't have a measuring tape) starting at your belly button and wrap around comfortably letting the tape cross itself just slightly when you get back to the belly button. Stay relaxed- don't suck in or try to tighten your abdomen while measuring. Once you have your measurement in inches you can take a look at the belt measurements listed for each belt size. I personally fall right into the "gap" where two sizes overlap (XS is listed as 25- 32 inches and small is listed as 30-37 inches) I tried the xsmall and the small and ultimately went with the xsmall because I was able to get a better snug fit when tightening the velcro strap. My personal recommendation if you fall into the gap (in this example 30-32) would be to choose the smaller of the two sizes.