Inventory space planner
Your inventory and each retainer hold a fixed number of slots, and one slot holds one stack up to the item's stack size. The same item split across bags or retainers takes a slot for every stack.
Open Inventory from the main menu, or summon a retainer at a retainer bell to open the retainer's inventory and move items between you. Items can be sold to a vendor for gil or listed on the market board through a retainer.