I bought an extra large size right before a trip to Moab Utah and used all 9070 cubic inches of space. Just to give you an idea of how big this bag is, I had a sleeping bag, pad, tent, clothes, cookware/stove, outerwear, my climbing gear (including a rope) my half shell mountain bike helmet and also my full face mountain bike helmet, a frisbee, and a slackline. The bag didn't even flinch under the load, and the zippers stayed solid even when they were under a bit of tension. This bag is going to be pretty heavy when full, but if you can wrestle it up, it carries with the backpack straps pretty well, though not for long distances. Buy one and take a sweet-action trip!