Minecraft wiki entry for Inventory, associated text: Most items can stack up to a maximum of 64 in one slot. Some items cannot stack, notably anything with a durability attribute (weapons, armor, and tools except for clocks and compasses), filled buckets, and potions. Certain items, such as snowballs, empty buckets, eggs, signs, honey bottles, banners, written books, and ender pearls can stack to only 16.