Minecraft modpack hosting sized by the pack you actually run

The author memory recommendation was measured on the client, with one person playing, and a good share of it goes to rendering, texture atlases and mods that live on the player side. None of that loads on the server.

Something else takes its place: every player keeps their own chunk radius loaded, and everything inside it is processed on every tick. A pack that fits in 6 GB for one person goes past that with six players in different corners, because that is six active regions instead of one.

On CurseForge the file that matters is the server pack, published in the files tab next to the client version. Without it you are left assembling the server from the client zip and cleaning by hand: shaders, minimap and interface mods break the boot.

On Modrinth the format is the .mrpack, an index of mods with hashes, resolved by mrpack-install or packwiz. Either way, open the startup script before the first boot: on Forge and NeoForge the memory lives in user_jvm_args.txt, and the author value rarely matches the step you bought.

Four things grow for different reasons: the mods folder, fixed once installed; the world, which grows with exploration; the logs, with operating time; and the backups, with the retention you choose. Only the first is predictable on signup day.

Every dimension the pack adds writes its own set of region files, so an exploration pack multiplies the map without anyone having explored much of the main world. Generating the map ahead of time avoids stutter in real time, but it charges the space all at once.

When the new version removes or renames mods, the blocks from that mod stay written into the chunks already visited. The loader warns that there are missing registries and asks for a confirmation that deletes those blocks, which can mean an entire base turning into air.

Take the full copy and test the upgrade on a separate instance with the world copied over: plans from 8 GB up include one subdivision, so it costs nothing extra. If it really does break, you can preserve the main world and reset only the mining dimension.