I'd have to measure my changing bag, but it's not too big. It's kind of cramped to say the least, but it's big enough to hold a box of film and two or three 8x10 film holders. It just takes a little more effort, and it's only a matter of managing your limited space better. There's also plenty of room for the film holders and a film developing drum.
Still, it packs up pretty small, and I've used it in the field (both at camps and the middle of nowhere) without a problem.