>>2837688 (OP)
>Do they just make up numbers?
Yes, oddly enough. Larger companies like Osprey use dimensional measurements to estimate volume. Some companies are strict about sticking to procedures (Atom Pack s for sure does this, Mystery Ranch too).
The procedure for measuring the internal volume of a backpack is ASTM F2153 (look it up; it’s a real thing). The pack is filled with 20mm pellets. Those pellets are then emptied into a separate container and measured. I think they weigh the pellets to calculate volume.
You’d think a larger company like Osprey would be more strict about internal procedures, but they’re just not. It kind of sucks, because if you have a pack that’s the perfect capacity but needs to be replaced, your new pack could be labeled the same but actually 15% smaller.
Treeline Review wrote an article about this. They’re wrong about ASTM charging for a test. It’s a procedure that anyone can follow. A materials testing lab will follow the procedure, and will have accreditation showing that they have credentials and traceable standards in place. But manufacturers can do their own testing, and since there’s no governing body for this type of test, they’re beholden to no one but their customers.
https://www.treelinereview.com/howtochoose/backpacking-backpack-volume
