How to Make a Tower Mob Grinder in Minecraft

What Is a Mob Grinder?

A mob grinder is a structure that spawns hostile mobs in a controlled environment, moves them to a collection point and kills them automatically or lets you finish them off for XP. Mob grinders produce gunpowder, bones, arrows, string, rotten flesh, spider eyes and occasionally rare drops like armor and weapons.

Unlike spawner-based farms that rely on finding a dungeon, dark room grinders work anywhere because they use the natural spawning algorithm. Build one high enough in the sky and you get consistent rates without needing to light up surrounding caves.

Choosing a Location

Spawn rates depend on the mob cap. Hostile mobs spawn in dark areas within 24-128 blocks of the player. The key is to make sure your grinder is the only dark place available:

• Over an ocean: The best location. Ocean biomes have no caves underneath, so the mob cap is not wasted on underground spawns. Build the grinder at Y = 200 or higher above an ocean.
• High in the sky: If you are not near an ocean, build at maximum height. Mobs spawn 24-128 blocks from the player, so position the spawning floors within that range and your AFK spot above or below.
• Underground: Works but requires lighting up all caves within 128 blocks, which is extremely tedious.

Basic Dark Room Design

The simplest mob grinder uses one or more dark rooms where mobs spawn on open platforms, then get swept into a central channel by water:

Spawning Floors

• Build a flat platform at least 17x17 blocks. Larger platforms (up to 33x33) produce more spawns but require more water channels.
• The ceiling should be exactly 2 blocks above the floor so mobs can spawn but endermen cannot (they are 3 blocks tall and will not spawn in 2-tall spaces).
• Leave the room completely dark. Do not place any light sources inside.
• Build 2-4 spawning floors stacked vertically with 3 blocks of spacing between each floor. More floors mean more spawns per cycle.

Water Channels

• Water flows 8 blocks in a straight line from a source. Use this to push mobs toward a central hole.
• Place water source blocks along one or two edges of each spawning platform. The current pushes mobs toward the opposite side where a trench leads to the central drop shaft.
• For larger platforms, divide them into sections of 8 blocks wide, each with its own water row.
• Signs or open trapdoors can hold water back at edges where you do not want it to flow.
• Use signs at the edge of the drop shaft to prevent water from flowing down while still letting mobs fall through.

The Drop Shaft

• All water channels converge on a central shaft that drops mobs to the kill chamber below.
• For an automatic kill grinder, make the drop 24 blocks. This kills most mobs on impact without player interaction.
• For an XP grinder, make the drop 22 blocks. Mobs survive with half a heart and you finish them with one hit to collect XP.
• Line the shaft with glass or solid blocks. Make sure there are no ledges where mobs can get stuck.

The Kill Chamber

At the bottom of the drop shaft, build a collection area:

• A 1x1 or 2x1 space where mobs land and stack up.
• If using fall damage (automatic mode), place hoppers below the landing spot connected to chests. Items are collected automatically.
• If using manual kills (XP mode), leave a gap at foot level so you can hit mobs' feet with a sword. A Looting III sword maximizes drops.
• Place a slab or carpet at the player's standing position to prevent mobs from hitting you through the gap.

Improving Spawn Rates

A basic grinder may feel slow at first. Here are ways to increase its output:

• Add more spawning floors: Each additional floor adds to the total spawnable area. Four floors is a good balance between build effort and output.
• Use trapdoors on the edges: Place open trapdoors along the water channels. Mobs see open trapdoors as solid blocks and walk onto them, then fall into the water. This speeds up mob movement significantly.
• Build over an ocean: Eliminates competing spawns in caves below.
• Light up surrounding terrain: If you are not over an ocean, torch up caves and surfaces within 128 blocks so mobs only spawn in your grinder.
• Use cats: Place cats on the spawning floors. Creepers flee from cats, moving them toward the water channels faster. This also prevents creeper explosions from damaging the farm.

Dealing with Spiders

Spiders are 2 blocks wide and can climb walls, which causes problems in mob grinders:

• Add iron bars or glass panes along walls. Spiders cannot climb these blocks easily because they break the flat surface the spider's AI needs.
• Alternatively, place a row of signs or buttons on the wall 2 blocks above the floor. This interrupts the climbing behavior.
• Some players add a spider filter, a 1x1 gap in the water channel that spiders cannot fit through, diverting them to a separate kill chamber.

AFK Spot Placement

Your AFK position determines the farm's efficiency:

• Stand between 24 and 32 blocks from the spawning floors. Mobs do not spawn within 24 blocks of the player, so you need to be far enough away.
• If you stand too far (above 32 blocks from spawned mobs), mobs may freeze in place and stop being pushed by water.
• Build a small enclosed platform at the correct height with a view of the kill chamber. Make sure it is lit and mob-proof.

Expected Output

A well-built 4-floor grinder over an ocean produces roughly:

• 500-800 gunpowder per hour
• 500-800 bones per hour
• 300-500 string per hour
• 200-400 arrows per hour (from skeletons)
• Occasional iron armor, bows and enchanted gear

These rates assume the grinder is the only spawnable area within 128 blocks and you are positioned correctly at the AFK spot.