Mob XP Farm — 3D Build Guide

The classic dark-room farm for zombies, skeletons and creepers: build it block by block in 3D, then watch it work.

A step-by-step 3D guide to the simplest effective vanilla XP farm in Minecraft Java Edition: a dark spawning room, water trenches that carry mobs to a 2×2 hole and a 22-block drop that leaves them with half a heart. Turn the model, open it up and count every block you need.

How to build the mob XP farm, step by step

Pick the spot and lay the floor — Build over an ocean or a flat plain, far from caves, and high up: the floor you stand on at about Y 200. Every dark cave within 128 blocks of you shares the same cap of 70 monsters, so height is what makes the farm fast. Pillar up and lay a 6×8 cobblestone floor — this is where you will stand.
Place a large chest — Put two chests side by side on the east edge of the floor: together they make a large chest. All the loot ends up here, and you open it from the side, standing next to it.
Six hoppers into the chest — Place six hoppers in a 3×2 block next to the chest, all pointing into it. The four farthest from the chest are the bottom of the drop shaft — the mobs land on them; the items travel hopper to hopper into the chest. Close the rest of the shaft's 4×4 base with cobblestone.
Build the kill window — On your side of the shaft, right above the hoppers, place two slabs in the top half of the block (click the upper half of the face) and full blocks above them; close the other three sides with solid blocks. You stand one block lower, so the ½-block gap is just below your eyes and shows only the mobs' feet: you can hit them, but their eyes are behind the block above — skeletons cannot see you to shoot and creepers do not ignite.
Light the floor — Put two torches on the floor so mobs do not spawn on it while you are away. No walls are needed here: the shaft walls and the slab window already keep the mobs in.
Raise the drop shaft — Build the walls of the 2×2 shaft straight up: 22 blocks of air from the hoppers to the top. A mob that falls 22 blocks takes 19 damage, so a 20-HP zombie, skeleton or creeper lands with half a heart — one hit, full XP.
Lay the spawning floor — At the top of the shaft lay a 20×20 cobblestone floor around the 2×2 hole. It is the bottom of the water trenches.
Platforms and trenches — On the floor, fill the four 8×8 corners and the outer ring two blocks high — these are the spawning platforms. Four 2-wide trenches, two blocks deep, stay open from the walls to the hole: the water goes in their lower block, open trapdoors in the upper one. 256 dark cells on top where mobs can appear.
Pour the water — Place two water sources on the bottom of each trench at its wall end, 8 in total. Water flows 7 more blocks, so in an 8-block trench it stops exactly at the edge of the hole and never pours down the shaft.
Hang open trapdoors over the water — In every trench cell, one block above the water, hang an oak trapdoor on the side of the platform next to it and open it: 64 trapdoors. A mob takes any trapdoor for a closed one, so the trench looks like solid floor — it walks straight in and falls into the water. Without trapdoors mobs keep away from the edge: walking next to water is expensive for their pathfinding.
Walls two blocks high — Two layers of walls around the room. A 2-block ceiling fits zombies, skeletons, creepers and spiders, but endermen need 3 blocks and will not spawn.
Roof and torches — Cover the whole room and put four torches on the roof, one per quarter. Inside must be pitch black: since 1.18 monsters in the Overworld spawn only at block light 0. Outside, the torches stop mobs spawning on the roof.
Go down and wait — Stand on the floor right against the window. Mobs spawn on the platforms, drop into the trenches, ride the water to the hole and land on the hoppers with half a heart. A sword hit kills one, and a fully charged hit on the ground, without sprinting, also deals 1 damage to the mobs next to it (the sweep attack) — enough to finish them. Each mob gives 5 XP (a baby zombie 12); from 0 to level 30 takes about 280 mobs.

Mob XP farm — questions

How high should a mob farm drop be?

22 blocks of fall. Fall damage equals the fall distance minus 3, rounded down, so mobs with 20 health — zombies, skeletons, creepers — take 19 and land with half a heart. From 23 blocks they die on their own and drop no XP; from 21 they keep 2 health. Before Java 1.21.5 the damage rounded up, so on older versions test the height in Creative.

Why are no mobs spawning in my XP farm?

Check four things: there is no light inside at all (in the Overworld block light must be 0 since 1.18); you stand 24 to 128 blocks from the platforms; there are no dark caves or surfaces within 128 blocks taking the mob cap of 70; and the ceiling is 2 blocks above the platforms. Mobs never spawn on glass, bottom slabs or trapdoors.

Why must the water trench be exactly 8 blocks long?

Water spreads 7 blocks from its source, so a source plus 7 flowing blocks reaches exactly the edge of the hole. In a longer trench the water stops short of the hole and mobs get stuck in the dry gap; in a shorter one the water pours down the shaft, and falling water cancels the fall damage.

How much XP does a mob farm give?

Every zombie, skeleton or creeper gives 5 XP, a baby zombie 12, and each piece of armour or weapon a mob spawns with adds 1–3. Going from level 0 to 30 takes 1395 XP, about 280 mobs. The real speed depends on how many caves are near the farm and how many floors it has — time ten minutes yourself.

Do I need Sweeping Edge or Looting?

No. In Java Edition a fully charged sword hit made on the ground, without sprinting, also deals 1 damage to the mobs right next to the target — the sweep attack — and that already kills everyone with half a heart. Looting only adds item drops.

Why are there open trapdoors over the water?

Mobs treat every trapdoor as closed, so an open one looks like solid floor to them. They walk onto it and fall into the water. Without trapdoors the cells next to water are expensive for their pathfinding, and mobs rarely step into the trenches on their own.

What happens to spiders and witches?

A spider has 16 health: if it falls freely, the 22-block drop kills it before you can hit it, so it gives no XP, but its string and spider eyes still reach the hoppers. Often a spider clings to the shaft walls and climbs down unhurt — then it needs a few hits. A witch has 26 health, lands with 7 and may drink a healing potion: usually two hits.

How a dark-room XP farm works

Hostile mobs spawn on any dark solid block with two blocks of air above it, within 24 to 128 blocks of a player. The farm gives them a large, perfectly dark room high in the sky and nothing else to spawn on for 128 blocks around, so the whole monster cap of 70 ends up inside it.

Mobs walk onto the open trapdoors over the trenches as if they were floor, drop into the water, the current carries them to the 2×2 hole in the middle and they fall 22 blocks. The fall takes 19 of their 20 health points, so they land on the hoppers with half a heart and die from a single hit through the slab gap. Because a player killed them, they drop XP; the hoppers collect the loot into the chests.