Minecraft wiki entry for Experience, associated text: Naturally spawned orbs always have an integer value of 1–11, 17, 37, 73, 149, 307, 617, 1237, or 2477. Fishing, breeding, and trading drop a single orb with a random value in the appropriate range. Breaking blocks, killing mobs and players, smelting items, and bottles o' enchanting calculate their total experience amount and then split it into values of 1, 3, 7, 17, 37, 73, 149, 307, 617, 1237, and 2477. Higher values are chosen first, so, for example, a total value of 1000 would be dropped as orbs with values 617, 307, 73, and 3. Note that while the first Ender Dragon in a world drops 12,000 experience, it is dropped in 10 waves of 1000 and one of 2000, so no orbs of value 2477 are dropped. Such orbs can only exist in the world via furnaces that have had a lot of traffic.