The largest Goodnites will stretch nicely to fit quite large bodies. When measuring bodies for diaper size, your widest point is more useful = the hip measurement. Even if somebody has a tiny waist, wider hips could result in diapers not fitting properly. Just get a pack and see if they fit
im around 34 inch waste and can fit them with room to spare(im 170 pounds currently) these are the new goodnites..everyone was saying they are supposed to be tiny but i found the opposite to be true..
i got the new boys design(its cute to btw) i was scared they were going to be too small both my wife and i fit in the new design with room to spare(both of us had several inches of extra room and they are long enough to cover our butts..the sides are way stretchier imo..i noticed they seemed thinner, but when wet they puffed up to a pretty awesome size honestly(try wearing one into the tub/shower to get an idea of the absorbency)..
i give the new goodnites design a solid A. i love the absorbency(its allot)
I have a waist of around 40" and the L/XL size fit me fine, I wouldn't call it a normal fit, but they work as intended and never leaked on me when I'm cautious, they last through the night without problems at all.
I would say at least 37 inches, but that's a bit of a blind guess. But this is for certain; because it is the intent of the product, GoodNites are pretty thin and thus will fit like underwear. So GoodNites don't quite give off that diaper-like fit that thicker adult tape-on diapers do, even with my 31" waist. But, they still serve the purpose they're meant to, so they'll get the job done if you fit in them.
Yeah, probably fine to about 36" they are all around better now, maybe a tiny bit shorter, but not enough to change how they fit. I'm personally like a 30-29" waist size and i have a lot of room left to stretch them.
Okay so two points:
1) Waist size is one thing, but like others have mentioned, your hip is the more important measurement.
2) Do you want them to fit, or just barely get the darn things on...Some people call getting them over their butts without ripping "fitting". (I don't) ....So it really depends on what you consider the definition of the word. Honestly I try every version of goodnites as they come out, but seriously 34"-ANYTHING waist or hip (or larger) is not "fitting" them, it's getting them "on". I'd say up to 28" waist/hip "fitting as intended", 30-32" waist "stretched but still a decent fit"...34"+ "not fitting as intended, causes difficulties, can rip with uncareful use" ...37"+ - "seriously if it gets on at all at that size, it's a thong, lol"