Sophisticated Backpacks capacity calculator

How backpack capacity works

Each tier adds inventory slots and upgrade slots, from 27 slots and one upgrade slot on the leather backpack to 120 slots and seven upgrade slots on the netherite one. Stack upgrades raise how much each slot holds, and unlike most upgrades they multiply each other: tier 4 twice is ×256, three times ×4,096. A backpack takes at most three stack upgrades. They also use up upgrade slots that other upgrades need, so a small backpack has to choose.

Items that normally stack to 16 get the same multiplier on their smaller stack, so they fill a quarter as many. Removing a stack upgrade is refused while a slot holds more than the smaller limit would allow.