How to Build a Mob Grinder for XP and Loot
Build a dark 18×18 room, let water push mobs down a 19.5-block drop, and finish them yourself for XP on top of bones, arrows, gunpowder and string.
This dark-room design needs no spawner, works over almost any Overworld biome, and runs day and night because its roof keeps the floor dark. The Mob Grinder Tower is this layout built block by block: about 2,200 blocks, 8 water sources and 6 Hoppers, with a 19.5-block drop and the half-slab kill window described below.
How the farm works
Hostile mobs spawn on four dark pads. Water carries them to a 2×2 shaft in the middle. The fall leaves most of them on two hearts or less, and you finish them through a window at the bottom. Hoppers under the landing spot send every drop to a Chest.
The last hit has to be yours. A mob drops XP only if it dies within 5 seconds of a hit from you or your tamed wolf, and some drops, such as Spider Eyes, need a player kill as well.
Choose the spot
Build high in the sky or out over the ocean. Every dark cave within 128 blocks of you takes slots from the same hostile mob cap of 70, and nothing spawns farther away than that. Over land, keep the ground more than 128 blocks below your waiting spot. Mob caps and chunk loading explains how to clear that sphere.
The biome at the farm's height decides what spawns.
| Biome at the farm | What spawns |
|---|---|
| Most Overworld biomes | Zombies, Skeletons, Creepers and Spiders, with the odd Witch and Zombie Villager |
| Desert | Husks and Parched need open sky, so none spawn. 4 in 5 zombie spawn attempts and half the skeleton ones are wasted |
| Snowy Plains, Ice Spikes | Strays need open sky, so none spawn. 4 in 5 skeleton spawn attempts are wasted |
| Swamp, Mangrove Swamp | 3 in 10 skeleton spawns are Bogged, which die in the fall and give no XP |
| Mushroom Fields | Nothing hostile. The farm stays empty |
Build the spawning room
- 1.Lay an 18×18 floor two blocks thick, from solid, opaque blocks. Mobs cannot spawn on glass, leaves, ice or bottom slabs.
- 2.Cut a channel 2 blocks wide through the top layer, across the middle in both directions. Where the channels cross, open a 2×2 hole through both layers for the shaft. That leaves four 8-block arms and four 8×8 pads: 256 spawning spaces.
- 3.Place two water sources at the outer end of each arm, 8 in total. Water spreads 7 blocks from a source on flat ground, so an 8-block arm ends with the stream on the lip of the shaft.
- 4.Build the walls around the outside of the 18×18 floor, so every arm stays 8 blocks long. Set the ceiling exactly 2 blocks above the pads. Zombies, Skeletons, Creepers and Spiders all fit under it. Endermen need 3 blocks of headroom, so none can spawn.
- 5.Roof it with bottom slabs. Mobs can't spawn on them, so the roof stays empty while it blocks the sky. Hostile mobs need block light 0, so keep every torch and lantern out of the room and shaft.
Slab the kill room's roof and any dark surface nearby. Mobs that spawn there never reach your chest.
Set the drop height
Mobs take 1 damage for every full block they fall past the first 3. Measure the drop from the channel floor, where a mob leaves the water, to the surface it lands on, which is the top of the slabs described in the next section. Anything from 19 to 22 blocks works. The Mob Grinder Tower's drop is 19.5 blocks, which deals 16 damage, the same as 19; 22 deals 19.
| Mob | Health | After a 19-block drop | After a 22-block drop |
|---|---|---|---|
| Zombie, Skeleton, Creeper | 20 | 2 hearts. One hit from a Stone Sword or better | Half a heart. One hit from any sword |
| Witch | 26 | 5 hearts. Keep hitting: it can drink a Potion of Healing | 3.5 hearts. Keep hitting |
| Bogged | 16 | Dead on landing: Arrows and Bones, but no XP | The same |
| Spider | 16 | Dies if it falls clear, with no XP or Spider Eye. One that catches the shaft wall climbs down unhurt: finish it at the window | The same |
After a 16-damage drop a Wooden or Golden Sword falls just short on a Zombie: its 2 armour points trim the sword's 4 damage to a little under the 4 health it has left. A mob that spawned wearing armour can take a second hit from a better sword too.
Stop short of 23: a 23-block drop deals 20 damage, enough to kill 20-health mobs outright, and a mob the fall kills drops no XP.
Keep the shaft dry: water of any depth cancels fall damage.
Kill window and collection
Make the landing floor of Hoppers: four under a 2×2 shaft, each pointing into the Chest or into another Hopper that does. Each Hopper costs 5 Iron Ingots and a Chest.
Cover those four Hoppers with bottom slabs. A Hopper still pulls in any item lying in the block above it, and the slabs give the pit a flat floor half a block higher, level with the bottom of the kill window.
Cut the kill window in the pit wall at the mobs' feet and keep it half a block tall: put a bottom slab in a one-block opening. About 1 zombie in 20 is a baby: under a block tall, it walks straight out of a one-block gap.
The slit has to start at the floor the mobs stand on, which is what the slabs over the Hoppers are for. An XP orb is half a block tall and can't climb. It slides out to you through a slit that is level with the floor. If the slit starts any higher, every orb stays in the pit and fades after 5 minutes.
Then lower the floor you swing from. Your eyes are 1.62 blocks above your feet, so from a floor level with the Hopper tops they sit too high to see into the pit. Swap the floor block in front of the window for a bottom slab and stand on it, a full block below the mobs' feet. Stand back from the wall and you look down through the slit at their feet, and nothing in the pit can see you. Crouch and your eyes come level with the slit, with the whole pit in reach. Baby Zombies and Spiders can see you then, but they can't reach across a wall one block thick. Adult Zombies, Skeletons and Creepers still can't see you, so no Creeper starts its fuse.
Where to wait
Nothing spawns within 24 blocks of a player, in a straight line. The pads are one block higher than the channel floor and at the window you stand one block below the landing slabs, so with the tower's 19.5-block drop the pads are only 21.5 blocks above your feet, and standing at the window stops almost the whole floor spawning. Make your waiting spot under the kill room, deep enough to put your feet 25 blocks below the pads: four blocks below the kill-room floor for the tower, two for a 22-block drop. From there every pad can spawn. Climb back up to the window to swing.
Don't wander off either: mobs more than 32 blocks from you stop walking about and can despawn at random, and past 128 blocks they vanish at once. That spot keeps the whole floor within about 30 blocks.
What you get
Drops per kill, without Looting:
| Mob | Drops | Only when you get the kill |
|---|---|---|
| Zombie, Zombie Villager | Rotten Flesh 0–2 | 2.5% chance of an Iron Ingot, Carrot or Potato; 8.5% of each piece of spawned gear |
| Skeleton | Arrow 0–2, Bone 0–2 | 8.5% chance of its Bow and each piece of spawned armour |
| Bogged (swamps) | Arrow 0–2, Bone 0–2 | Arrow of Poison 0–1, which this farm never gets: the fall kills Bogged |
| Creeper | Gunpowder 0–2 | Nothing extra |
| Spider | String 0–2 | Spider Eye 0–1 |
| Witch | Redstone Dust 4–8, plus 1–3 rolls of 0–2 Glowstone Dust, Sugar, Spider Eye, Glass Bottle, Gunpowder or Stick | 8.5% chance of the potion it is drinking |
Each adult mob here pays 5 XP when you land the kill, plus 1–3 for every piece of gear it spawned with. Level 30 from zero takes 1,395 points, about 279 kills of mobs with no gear. The XP calculator works out any other target.
Looting adds 0–1 per level to every count in the middle column. At Looting III it also lifts the rare-drop chance for Zombies and Zombie Villagers from 2.5% to 5.5%.
Fixing a farm that misbehaves
- Mobs arrive at full health. An arm is shorter than 8 blocks, so water spills down the shaft.
- Mobs pile up short of the shaft. An arm is longer than 8 blocks, so the stream stops before the lip.
- Drops pile up on the landing floor. A Hopper points the wrong way and has filled up.
- No XP reaches you. The slit starts above the floor the mobs stand on. Slab the Hoppers so the two are level.
- Spawns slow down. Mobs left alive in the pit still count toward the mob cap, so swing often.
What to build next
If you find a zombie or skeleton dungeon, the spawner XP farm needs no platform. For gunpowder alone, build a creeper farm. How to get XP fast compares this farm with every other source of levels.