A cobblestone generator is just water and lava set up so they keep running into each other. When flowing lava meets water, the lava turns into cobblestone. That new block sits between the two streams and keeps them apart until you mine it. Then they touch again and another block forms in the same spot. The simplest build is a short trench with water poured in one end and lava in the other. That's genuinely the whole thing.
There's one rule you can't break: the water has to meet the lava's flow, never the lava source block you poured out of the bucket. If flowing water reaches the source itself, the source turns into obsidian and your lava's gone. Everything below is built to avoid that. Oh, and none of it works in the Nether. Water evaporates the moment you place it there, so you can't build a cobblestone generator in the Nether.
How a cobblestone generator works
What you get depends on which part of the lava the water touches, and from which direction:
| What meets what | What you get |
|---|---|
| Flowing lava and water meeting side by side, on the same level | Cobblestone |
| Lava flowing down into water from above | Stone |
| Flowing water reaching a lava source block | Obsidian, and the lava source is destroyed |
Distances matter because lava is lazy. In the Overworld it only spreads 3 blocks sideways from its source, and it crawls along at about one block every 1.5 seconds (30 game ticks). Water is much quicker. The trench lengths below are what it takes for the two streams to actually reach each other.
How to make a cobblestone generator: the basic trench
This is the classic pistonless build from the Minecraft Wiki's cobblestone farming tutorial: a straight trench with a source at each end. Picture the trench as ten squares in a row, numbered 1 to 10.
- Dig a straight trench 10 blocks long.
- Pour your water bucket into square 1 first, and let it run. It runs down the trench toward the far end. Don't touch the lava yet. If the lava starts flowing before the water gets to it, it can "resist" the water and you won't get any cobblestone.
- Then pour your lava bucket into square 10. It creeps back toward the water, slowly.
- Wait for them to meet. Cobblestone forms right next to the lava.
- Cap the lava with a slab or another non-flammable block (not wood). That keeps the lava from destroying the cobblestone drop when you mine it, and it stops you stepping into it.
- Stand beside the trench, away from the lava end, and mine it. That's the safer spot. Leave the lava uncapped and some of the cobblestone you mine can end up in it. A fresh block forms in the same square once the lava flows back in.
Don't stand at the lava end or anywhere the lava can flow, and keep that lava capped. One block of cover is cheap. Your only lava bucket isn't.
Simple cobblestone generator: the 5-block version
If you're short on space (or on blocks to dig into, which is every skyblock island ever), the wiki's simplest design is smaller. Picture five squares in a row:
- Dig a trench five squares long, with one square left open in the middle. That open square is where the cobblestone will form.
- Pour water first, at the end nearer that open square, and let it run.
- Pour lava at the other end.
- Mine the cobblestone that forms in the open square. That's where the flowing water and flowing lava meet, and a new block appears there every time you clear it.
Same rules as the long version. Cap the lava with a slab or a non-flammable block, and mine from beside the trench, away from the lava end. Then give the lava a moment to flow back after each block.
Why it's an infinite cobblestone generator
Neither source block gets used up. Only the flowing parts of the water and lava meet, and the cobblestone forms where they meet. The sources themselves just keep flowing for as long as nobody touches them. That's why one bucket of each gives you as much cobblestone as you're willing to mine.
So what does eat your lava? Two things:
- Scooping the source back up with a bucket. That removes the lava source entirely. So don't do it unless you're really moving the generator.
- Letting water reach the source. That's the obsidian mistake, and it destroys the source.
My advice: decide where the generator lives before you pour anything, and build it once.
Automatic cobblestone generator with a piston
An automatic generator swaps you out for a piston. You don't mine the fresh cobblestone. The piston pushes it out of the way, the water and lava touch again, and a new block forms, ready to be pushed next.
The easiest one to start with is the wiki's basic piston generator, which runs on a clock:
- The core: a basic water-and-lava core, with the cobblestone forming in one square.
- The piston: placed facing the square where the cobblestone forms.
- The clock: a simple repeater clock that fires the piston over and over. Set the repeaters to at least 14 ticks. The cobblestone needs time to form, and anything faster just makes the piston thrash at nothing.
Every time the piston fires, it shoves the new block out into a line, and the line gets longer with each push. You mine it down whenever you need blocks. Watch the length, though. A piston can only push 12 blocks, so the row jams once it's 13 cobblestone long. Mine it down before then, or cap the end of the line with an unpushable block like a furnace.
There's also a detector version that uses a sticky piston and only fires when a block actually shows up. It's neater, but the clock build is the one to get your head around first if redstone's new to you.
The stone generator variant
If lava flows down into water from above, you get plain stone instead of cobblestone. Stone mines slightly faster than cobblestone, but the lava has to sit directly above the spot where the block forms. That's why stone generators are almost always built around a piston that pushes the stone out from the front once it forms.
Cobblestone generator on Bedrock vs Java
As of October 2026 the basic build works the same on both editions. Same lava-meets-water rule, same trench, same obsidian trap, and same no-Nether catch. Whichever edition you play, follow the steps above as written.
Common cobblestone generator mistakes
- Turning your lava into obsidian. Flowing water reached the lava source instead of the lava flow. Check where the water goes before you pour the lava, not after.
- Pouring the lava first. If the lava's already flowing when the water arrives, it can "resist" the water and no cobblestone forms. Water first, let it run, then lava.
- Losing the drop to the lava. If the lava's uncovered, it can destroy the cobblestone you just mined. Put a non-flammable block over it.
- Mining too fast. Lava moves about one block every 1.5 seconds, so the replacement isn't instant. Swing again too soon and you're hitting empty air. Let it refill.
- Standing where the lava flows. Mine from the side, and cap the lava so there's nothing to fall into.
- Building it in the Nether. The water evaporates as soon as you place it. Build in the Overworld.
Why skyblock players build one first
Skyblock starts you on a tiny island with almost nothing, so there's no ground to go digging for stone in. Cobblestone is how you get tools, a bigger island and room to work, and a generator is how you keep it coming. That's why most skyblock players build one before they try anything clever. My guide to how to play skyblock walks through the whole first hour, from getting the map to replanting your tree and setting up the generator safely. If you'd rather play skyblock on a server than on your own map, here are the best skyblock servers and what each one does differently.
Playing a different flavour of the genre? One Block doesn't give you an island to build on at all, so the run goes differently. Here's how One Block Minecraft works. And on Terraria's sky island, getting stone is a whole different problem, covered in my Terraria skyblock seed guide.
Cobblestone generator FAQ
Do cobblestone generators still work?
Yes. Lava meeting water and turning into cobblestone is one of the oldest, most stable mechanics in Minecraft, and the trench builds above still work today. The one place they've never worked is the Nether.
What is the fastest way to generate cobblestone?
Automate it. A piston generator keeps running while you do other stuff, and bigger multi-piston designs push out more blocks each cycle than you'll ever get by hand. If you just want building blocks and don't care whether they're cobblestone, a stone generator's blocks also mine a bit faster.
Can you make a generator without water?
Not for cobblestone. Swap the water for blue ice and use soul soil (not soul sand), and you get basalt instead, using the same principle.