How to build a slime farm in Minecraft 26.3

Slimeballs are the quiet enabler of advanced Minecraft. They craft into slime blocks and sticky pistons, the two components behind flying machines, hidden doors, and most compact redstone contraptions, and into leads for moving animals. If you have ever wanted to build serious redstone, you have wanted a slime farm.

The catch is that slimes spawn in two specific, awkward situations, and a farm targets one of them: slime chunks deep underground. Find one, dig out the spawn floors, and you have an endless slimeball supply feeding your redstone projects.

This guide targets Minecraft 26.3 Java Edition. It is a spoke of the farm guides hub, and the slime blocks and sticky pistons it feeds power the builds in the redstone handbook.

What a slime farm produces

• Slimeballs, which craft into slime blocks, sticky pistons, leads, and magma cream for potions.
• The raw material for flying machines and compact redstone, since slime blocks move connected blocks with pistons and, unlike honey blocks, actually stick to them.
• A steady supply once the spawn floors are cleared and correctly placed.

Two completely different spawn mechanics

Slimes spawn under two rule sets that share nothing but the mob. Treating them as one mechanic is the most common way a "finished" farm produces nothing.

Slime chunks, below Y level 40:

• Only about 1 in 10 chunks in the world qualify as slime chunks at all.
• Inside a slime chunk, slimes spawn below Y=40, and they spawn at any light level. This is the unusual part: nearly every other hostile mob needs darkness, but slime-chunk slimes don't check light at all.
• Java Edition spawns them in groups of four at once, on any valid floor block, anywhere in that chunk below Y 40.

Swamps, between Y 51 and Y 70:

• Slimes spawn in swamp biomes between Y=51 and Y=69 inclusive, on the surface, at night.
• Unlike slime chunks, light matters here: the spawn requires a light level of 7 or less.
• Moon phase matters too: swamp slimes spawn most often on a full moon and never on a new moon, since the game rolls the moon's illuminated fraction against a random chance each attempt.

These are not two versions of the same rule with different numbers. One ignores light and lives deep underground on a seed-fixed chunk; the other needs darkness, night, and a specific biome, and gets better or worse by the day depending on the moon. A slime-chunk farm runs at any time, any weather, once built; a swamp farm is easier to set up but is only productive at night and worse around a new moon. This guide focuses on the slime-chunk method since it is the reliable, always-on option.

Finding a slime chunk without guessing

Slime chunks are not random per session: in Java Edition they are derived mathematically from your world seed plus the chunk's coordinates, so the same seed always produces the same set of slime chunks, every time you regenerate or revisit that world. That determinism is exactly why a slime-chunk farm is worth the dig: once you've found one, it stays a slime chunk forever.

Two ways to identify one:

• Compute it from your seed. Because the slime-chunk check is just a function of seed and chunk coordinates, tools that take your world seed as input can tell you exactly which chunks qualify, without you digging anything. This guide won't point you at a specific one, any tool built on the documented seed formula will do.
• Confirm in-game. Press F3+G to draw chunk borders so you know exactly which chunk you're standing in, then dig out a large flat area below Y=40 within those borders and wait. If slimes start appearing, you've confirmed the chunk. If nothing spawns after a reasonable wait with the area cleared and other spawn spots dark, you're very likely in the wrong chunk, not just having bad luck, since slime-chunk spawning ignores light and should not be this shy in a real slime chunk.

Size mechanics: only small slimes matter for slimeballs

Slimes come in three sizes: large, medium, and small. When a non-small slime dies, it doesn't just disappear, it splits into 2 to 4 smaller slimes one size class down: a large slime's death spawns mediums, and a medium's death spawns smalls. Only the small size actually drops slimeballs; large and medium slimes drop nothing on death besides their split.

That means every slime your farm spawns has to be cycled down to small before it produces anything collectible. A kill chamber built to handle only the size that walks in (large) and not the two waves of smaller slimes that result from splitting will lose most of its potential yield, since a single large slime can end up producing eight or more small slimes across two splits before any slimeballs actually drop.

Once you have a small slime, killing it drops 0 to 2 slimeballs, averaging 1.0 per kill. Looting III raises that to 0 to 5, averaging 2.5, roughly two and a half times the unenchanted rate, so a Looting sword on your kill weapon (or a Looting-enchanted setup if the kill is automated some other way) meaningfully changes output per kill, not just per session.

How it works

1. Find and confirm a slime chunk, below Y=40.
2. Dig out spawn floors. Hollow large flat layers across the whole chunk, stacked with a few blocks of headroom, so slimes have lots of spawn space. Light doesn't matter here.
3. Light everything else. Slimes ignore light, but you must light nearby caves so other mobs, which do care about darkness, don't steal the mob cap.
4. Funnel and kill. Slimes wander, so water streams or a sloped floor push them to a collection point where you kill them, handling all three sizes as they split down to small.

Building it

1. Clear the chunk. Mine out several wide, flat spawn floors within the confirmed slime chunk, entirely below Y=40, aligned to the chunk borders (understanding chunk borders helps you stay inside the right chunk and not spill spawn floors into a neighboring, non-slime chunk).
2. Light the surroundings. Torch or seal every cave and dark space near the farm so the mob cap is not wasted on zombies and skeletons, which do check light and will out-compete slimes for spawn slots if left unlit.
3. Water funnels. Add water streams on each spawn floor that carry slimes to a central drop or channel.
4. Kill chamber sized for all three sizes. Route slimes to a chamber where you kill them, remembering a large slime splits into mediums which split into smalls, two full generations before any slimeballs drop. Hoppers below feed chests.
5. AFK spot within normal mob-spawning range so spawns keep running while you wait or work nearby.

Common mistakes

• Building above Y=40. Slime-chunk slimes only spawn below Y=40. Even a few blocks too high and nothing spawns, regardless of how well-lit or dark the room is.
• Not confirming the slime chunk. Digging out the wrong chunk produces zero slimes no matter how correct everything else is. Verify with F3+G and a seed-based chunk check, or a patient in-game wait, before committing to the full build.
• Leaving caves unlit. Other mobs eat the mob cap and starve your slime spawns, since slimes share the general hostile mob cap with zombies, skeletons, and everything else nearby.
• Kill chamber that only handles big slimes. Slimes split into 2-4 smaller slimes per generation, and only the small size drops slimeballs; a funnel that loses track of the smaller splits loses most of the farm's actual output.
• Confusing the swamp method with the slime-chunk method. They have different Y ranges, different light rules, and one depends on the moon phase. A design built for one will not work if you accidentally try to run it under the other biome's rules.

Rates and optimization

There is no wiki-published slimeballs-per-hour figure for a slime farm, because actual throughput depends on how much spawn floor area you've dug out, how effectively you've suppressed competing mob spawns, and how quickly your kill chamber processes the size-splitting cascade; treat any specific hourly number you see elsewhere as an estimate for that particular build, not a guarantee for yours. What is fixed is the per-kill math: an average of 1.0 slimeball per small slime unenchanted, rising to an average of 2.5 with Looting III, and a large slime requiring two full split generations before any of that yield actually appears.

To improve real output:

• Clear and light a wide area so nothing else spawns nearby, giving more of the mob cap to slimes.
• Dig out more spawn floors to increase valid spawn space within the chunk; more floor area means more concurrent spawn attempts.
• Use a Looting III weapon on the final small-slime kill step to roughly two-and-a-half the slimeball yield per kill.
• Consider a mob switch elsewhere in the world to suppress general hostile spawns and hand more of the cap to the farm; see the mob switch guide.

For most players, one slime-chunk farm supplies all the slimeballs their redstone will ever need.

Slime-chunk slimes don't care if the room is dark. They care if the room is deep enough.

Frequently asked questions

How do I find a slime chunk?

Slime chunks are derived from your world seed plus each chunk's coordinates, so the same seed always has the same slime chunks, about 1 in 10 of all chunks. A tool built on that seed-based formula can compute them directly. In-game, use F3+G to confirm chunk borders, dig out a large flat area below Y=40 within one chunk, and wait to see if slimes spawn.

What Y level do slimes spawn at?

In slime chunks, slimes spawn below Y=40 at any light level. In swamps they spawn between Y=51 and Y=69, on the surface, at night, and only at light level 7 or below. These are separate rule sets, not the same rule at two ranges.

Why is my slime farm not spawning slimes?

The usual causes: the farm is above Y=40, it isn't actually in a slime chunk, or nearby caves are stealing the mob cap from other, light-sensitive mobs. Confirm the chunk with F3+G plus a seed check or an in-game wait, dig strictly below Y=40, and light everything around the farm.

Do slimes need darkness to spawn?

Not in slime chunks. Slime-chunk slimes spawn at any light level, which is genuinely unusual among hostile mobs. Swamp slimes are the opposite: they need light level 7 or below, night, and spawn best on a full moon and never on a new moon. Light everything around a slime-chunk farm anyway, not for the slimes, but so other mobs don't compete for the mob cap.

Does Looting affect slimeball drops?

Yes. An unenchanted kill on a small slime drops 0-2 slimeballs averaging 1.0; Looting III raises that to 0-5 averaging 2.5, about two and a half times the base rate. Only small slimes drop slimeballs at all; large and medium slimes drop nothing but their split.

A slime farm unlocks the sticky pistons and slime blocks that serious redstone runs on. With a steady slimeball supply, the flying machines and contraptions in the redstone handbook become buildable, and the farm guides hub covers every other farm your base will want.