How much RAM does a modded Minecraft server need? Measured (2026)

1What each modpack used on a real server

Seven packs, installed from CurseForge or Modrinth on the same kind of 16 GB machine, one server at a time, with nobody online.

Loaders: NeoForge 21.1.251 for All the Mods 10, 21.1.250 for StoneBlock 4 and 21.1.172 for Pixelmon; Forge 47.4.0 for All the Mods 9 and 47.4.20 for Better MC 4.

Better MC 2 v40 (Fabric, 289 mods) and SkyFactory 5 5.0.8 (Forge) started too; their memory wasn't recorded, so they're only in the startup table below.

2Why a server needs about 2 GB more than its heap

Java keeps the world, players and items in its heap, the -Xmx you set. The loader and every mod's classes, mixins and compiled code sit outside it. Playkeeper starts servers with Aikar's flags, which claim the whole heap at start (-Xms equal to -Xmx, with AlwaysPreTouch), so the memory used is the heap plus that outside part. With 300 to 460 mods, the outside part came to 1.6 to 2 GB on every big pack we ran:

• All the Mods 10: 5.9 to 6.3 GB used with a 4.3 GB heap, and 10.2 GB with an 8.3 GB heap.
• All the Mods 9: 6.2 GB with a 4.6 GB heap.
• Better MC 4: 11 GB with a 9 GB heap.
• The Pixelmon Modpack: 3.5 to 3.8 GB with a 2.9 GB heap, since 13 mods need much less room outside it.

So on a plan or a VPS with 8 GB in all, give a big pack a heap of about 6 GB, not 8. A heap as big as the whole machine gets the server killed once it grows into it.

It also means used memory says little about need: All the Mods 10 used about 4 GB more with the bigger heap, with nobody online.

3The smallest heaps we tried

All the Mods 10 ran out of memory at its first start with a 2 GB heap, which is what 4 GB gives a pack that size. It started with 4.3 GB, and All the Mods 9 with 4.6 GB; nothing in between was tried. That's a floor with nobody online: players exploring new chunks, farms and machines need more, which is why All the Mods 10 and StoneBlock 4 ask for an 8 GB heap in their own files.

• A big pack, just you: 8 GB.
• A big pack and up to four friends: 12 GB, which gives Java the 8 GB heap those packs ask for.
• A big pack and more friends: 24 GB, from the sizing guide.
• A small pack like the Pixelmon Modpack: 4 GB.

4How long each pack took to start

From a fresh install to a server players can join, and the Done time each server printed in its log.

Minecraft's Done timer starts after the mods have loaded, so it leaves most of a modded server's startup out. StoneBlock 4 restarted in 50 seconds, with everything already downloaded, while its log said Done (2.041s).

5Mods that stop a first start

Some first starts fail for reasons that have nothing to do with memory: a mod made only for players' games.

• FTB StoneBlock 4 1.22.0: statuseffectbars stops the server with "invalid dist DEDICATED_SERVER". Delete its jar from mods.
• Better MC 5: delete Better Grassify and Distraction Free Recipes before the first start, as its page says.
• All the Mods 9 1.1.1: Mekalus, a shader mod, crashes a server set up from the pack's player files. ATM's server files leave it out, so start from those.
• Better MC 2 v40: it won't start without Mod Menu, although CurseForge marks that mod for players only.

6How we measured

• The machine: a 16 GB Linux cloud VM with 4 vCPUs, the same kind for every run, one server at a time.
• The install: Playkeeper installed each pack from CurseForge or Modrinth into its Docker container (itzg/minecraft-server, with Java 17 for Minecraft 1.20.1 and Java 21 for 1.21.1) with the memory shown.
• The heap: Playkeeper sets -Xmx to the memory minus room for the loader and mods: a quarter of the memory, or 1 GB plus 6 MB per mod on Forge and NeoForge, whichever is more, and at most half.
• The flags: Aikar's flags with G1, which set -Xms to the -Xmx and pre-touch the heap, so the whole heap counts as used from the start.
• Memory used: the container's memory without file cache, as docker stats shows it, read once the server was online.
• Times: from Playkeeper's log of each install.
• Runs: one per setting, two for All the Mods 10 at 8 GB, so treat small differences as noise.