my son be very skinny and only 23 lb . I measure he and he should have easily fit in the small size . unfortunately , even on the largest snap , the Smalls cut into he skin on he leg . I order the Mediums and they be still tight on he skinny leg . to add to the problem , the two time he have pee in they , they have completely leak all over he pants . we have now spend $ 80 on pants that do not fit and do not work . I highly DO NOT recommend .