*The smaller number is unstretched.  The larger number is fully stretched. 

Please note that size charts are notoriously difficult to make.  This one is based partly on the size chart written by the previous owner, partly my experience on my daughter, and partly on the experience of my customers.  I've seen 16 pound babies wear a large and 28 pound babies wear mediums.  The perfect fit is determined more by your baby's shape than her weight or even measurements. 

In general, I don't recommend sizing up.  While a large may technically fit at 20 pounds, for most babies this will produce a droopy-butt appearance.  If you're looking for that "like it was made for my baby" fit, then a medium is probably the best choice between 18-23 pounds.  If cost is more important than appearance, though, a large will do just fine for most babies starting around 19 pounds. 

To measure your baby's thighs, wrap a fabric tape around her thigh where her diaper normally sits.  Do the same for the waist.  For the rise, measure from her belly button down between her legs and up her back to where her belly button would be if we had them on our backs!