The number one thing to know is, these hot shorts are STRETCHY. Very stretchy. Stretchy enough that I can wear any of the three sizes. So, whether you are shopping for yourself or shopping for a friend who's butt you've never measured, none of the sizes will be a total DISASTER. But, much like goldilocks and the three bears, one of the sizes will be more "just right" than the others.
I DO have a size chart, but as Heidi the web developer pointed out, "Looking at this size chart, I'd automatically never order any Snacks because the XL is a 29" waist and I have a 36" hips." Yet, friends of mine with 36" or larger waists actually fit quite nicely into the XLs, because of the marvelous stretch. AND I myself, with the flattest white-girl ass in town, can wear the XLs (but they do kind of loosen up after the first hour of wearing, making them not "just right").
The main things to remember are:
Really what I need to do is invite a bunch of girls with all different shapes and sizes of ass to come over to my house, ply them with cupcakes and champagne, and then photograph a representative from dress sizes 2-12, wearing each size of Snacks, so you could just pick an ass size that seems like yours and look at how each of the Snack sizes fits on that ass (your designated control group ass) and order with a little more peace of mind than you have now.
As a visitor to the Snacks website has already pointed out, there are a lot of hot asses out there that are larger than a size 12. She's right, and those asses deserve Snacks. Right now, American Apparel, who I get the shorts from, doesn't make a larger size than the XL that fits a size 12. (And weirdly they've just introduced both XS and XXS, for tiny wood nymphs perhaps? The medium already barely covers my ass crack! And I'm a size 4! [Albeit, that's on the new vanity sizing chart from companies like Gap or Banana Republic who flatter us with artificially shrunken size tags.])