Minecraft wiki entry for Units_of_measure, associated text: 1 full hopper = 5 stacks = 320 items.
1 stack of blocks = 9 stacks = 576 items when completely uncrafted.
1 full dispenser or dropper = 9 stacks = 576 items.
Mining capacity of an unenchanted diamond pickaxe = 24 stacks 25 items = 1561 items.
1 full chest = 27 slots or 27 stacks = 1,728 items.
Mining capacity of an unenchanted netherite pickaxe = 31 stacks 47 items = 2031 items
1 inventory = 37 stacks = 2,368 items, when the offhand is included.
1 full double chest = 2 chestfuls = 54 stacks = 3,456 items.
Note: The phrase "double chest" is often shortened to "dub"; e.g. "a dub of cobblestone", meaning 54 stacks.
1 chestful of shulker boxes = 27 chestfuls = 729 stacks = 46,656 items.
1 double-chestful of shulker boxes = 54 chestfuls = 1458 stacks = 93,312 items.