Gear Guy

How do companies measure the volume of a backpack?

When a pack manufacturer specifies a volume for a certain pack, do they mean the main compartment only or does the number include all the outside pockets as well? It seems that a 40-liter pack from one brand is not the se size as a 40- liter from another. Kenneth Toronto, Ontario

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In the outdoor-gear world, almost all measurements and specifications have to be taken as more of an advisory than a last word. One person may sleep warmly in one 30-degree bag, but only marginally warmly in another; some size-nine boots fit me fine, others are too tight. The same is true with packs. Some makers check the volume with the storm collar all the way up, some don’t. Most, I think, figure in their pockets, but perhaps not all. And there are various methods for measuring the volume itself-filling them with dried beans, then figuring the volume of the beans and other decidedly non-scientific techniques included. And keep in mind that from a strictly subjective point of view, two packs of the same true volume may look to be of different sizes due to their shape-tall and narrow versus short and squat. So while two different packs may be rated at the same volume, and that volume may represent an honest assessment on the part of the maker, they could vary in practical terms by ten or 20 percent.

For that reason, it’s probably best to compare packs of similar rated sizes carefully. Take some time to have a salesperson round up a sleeping bag, camp cookset, and maybe a few jackets. Fill the pack at least partway full of these items and do the same with other packs you’re considering. The “real” volume-meaning both how much actual space there is, plus how usefully that space is shaped- will become apparent soon enough.