Minecraft seed map guide
This page is the reference companion to the seed map: what each number means, how the coordinate systems relate, and where the limits of seed-based prediction sit.
Coordinate systems
- Block coordinates are what the F3 screen shows and what /tp accepts.
- A chunk is 16×16 blocks. Chunk coordinates are block coordinates divided by 16, rounded down.
- A region file covers 32×32 chunks, or 512×512 blocks, and is named r.X.Z.mca in the world save.
- The world border sits at ±29,999,984 blocks on each axis.
Overworld and Nether coordinates
The Nether is compressed 8:1. Dividing an Overworld X and Z by eight gives the Nether position a portal there would link to, and multiplying by eight does the reverse. Y is not scaled. This is why Nether tunnels are the fastest long-distance travel in the game.
Slime chunks
Slime chunks depend only on the world seed and the chunk coordinates — no biome or terrain data is involved — so they can be computed exactly from the seed alone. Slimes spawn in them below Y 40 regardless of biome. Swamps also spawn slimes at night, independently of slime chunks.
What a seed map cannot tell you
- Anything a player has changed. A seed map shows the world as generated, not as it is now.
- Chest contents. Loot is rolled when the chest is first opened, not at world generation.
- Mob positions, which are runtime state rather than generation data.
- Anything about a modded or datapack-modified world, unless the modification leaves vanilla generation untouched.
Accuracy and versions
A seed map is only as accurate as the generation rules it implements, and those rules change between Minecraft versions. Always select the version your world was created in — not the version you are currently playing, if the world was made earlier and carried forward.