Backpack’s volume capacity and weight capacity are very different features. The former can be measured and it is exact. The latter is based on technical durability and on comfort level and therefore it is never exact.
What’s the Difference Between a Woman’s and a Man’s Backpack?
Although hiking, backpacking, and mountaineering packs are mostly unisex, they are sometimes built separately for men and for women. Here you can read more about their differences.