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Minecraft Modpack RAM

Forge / Fabric / NeoForge

Enter your PC memory and mod count to estimate a starting allocation for your launcher.

Your setup

Total installed RAM, not currently free memory.

0–500
Startup settingsG1GC

Start with G1GC. This ZGC preset targets Java 21. Select the Java version in your launcher or on your server.

Start with this allocation

≈ 7 GB

Allocate to your game in the launcher · 7,168 MB

Minecraft
7 GB
OS and other apps
9 GB

This is an estimate from your settings, not a measurement of your game. Check it with your own pack.

Launcher argumentsView code
-Xmx7168M -XX:+UnlockExperimentalVMOptions -XX:+UseG1GC -XX:G1NewSizePercent=20 -XX:G1ReservePercent=20 -XX:MaxGCPauseMillis=50 -XX:G1HeapRegionSize=32M

Where to use it

Find the memory setting in your launcher and set 7,168 MB. If you use JVM arguments, replace the existing memory flags with the copied line. Keep only one -Xmx flag.

Questions & reference

How accurate is this memory estimate?

This is a starting estimate based on the pack type, mod count, and player count. It does not measure your game. Packs with the same mod count can use very different amounts of memory. Check actual memory use and a performance report after starting, then adjust the allocation.

Why should I leave memory outside Minecraft?

The -Xmx flag limits the Java heap. Your OS, other applications, and Java itself also use memory outside that heap. The estimate leaves headroom, but you should check actual use on your PC or hosting plan.

Where do I put launcher arguments?

In Minecraft Launcher, open Installations → Edit profile → More Options → JVM Arguments. In other launchers, open the pack’s memory or Java settings. Replace existing memory flags and keep only one -Xmx.

Should I use G1GC or ZGC?

Start with G1GC and compare results with your own pack. Aikar’s flags are a server preset, not a promise of higher FPS. The ZGC preset on this page targets Java 21 and is unavailable for legacy 1.12.2 / 1.16.5 packs. This generator does not install or switch Java.

More tools in this section

Game and server RAMMinecraft startup flagsRead a performance reportCheck a Java version error