Camelbak says it's a 722 cu. in. pack but I think that number is for it's expanded size. When it's not expanded out, it seems to be smaller than the MULE. The main pocket is huge...even when unexpanded. The outer pocket is around the same size as the outer pocket of the MULE. Expanded it holds a bunch of stuff. Almost as much as the HAWG. It doesn't have any kind of compression system like the others but that makes it smoother and less likely to catch stuff, like branches, while riding. It does mean that any excess stuff has to go inside but it also means that there's less likelyhood of finding out you jacket is 4 miles up the trail