Pack Size Pack volume (size) is measured in liters or cubic inches. Using a pack that is too small in volume makes it hard to work out of and often forces you to attach items to the outside of the pack. Loose items will make your pack unbalanced and less comfortable to carry. Guide interpretation: more room is better.\r\n\"A mountaineering pack should have a clean profile. By strapping and hanging things on the outside of your pack, you run the risk of losing them and it\'s just poor form ... looks sloppy.\" Peter Whittaker