Minecraft
World Size on Disk
A Minecraft world's size on disk is decided almost entirely by how far the border is set, because that is what caps how much terrain can ever be generated. Everything else is a rounding error next to the square of the radius.
How this is calculated
The border is square, so the generated area is the radius doubled and squared, divided into sixteen-block chunks. Each saved chunk is around 45 KB on 1.17 and older and around 85 KB from 1.18 onward — the world got fifty per cent taller in that update and the saved chunk grew with it. The Nether runs at one eighth the scale, so the same border encloses an eighth of the distance in each direction and a sixty-fourth of the area, which is why it contributes far less than people expect.
The arithmetic
- chunks = (2 × border radius ÷ 16)²
- nether chunks = (2 × radius ÷ 8 ÷ 16)² · end ≈ 2% of overworld
- disk = chunks × KB per chunk (45 KB pre-1.18, 85 KB from 1.18)
What people get wrong
This assumes the world is fully generated out to the border, which is the worst case and the right number to budget for if you pregenerate. A world that players have merely wandered through will be much smaller. Working the other way, region files allocate space in 4 KB sectors, so a thinly explored world takes more room than its chunk count suggests — the pregenerated estimate and the sparse reality converge from opposite directions.