How to allocate more RAM to Minecraft in any launcher

Your modpack stutters, hangs on the loading screen or crashes with OutOfMemoryError, and the advice is always the same: give Minecraft more RAM. The setting is easy to change once you know where your launcher hides it. Here's the exact screen for each one.

Before you start: how much RAM your computer has

You can't give Minecraft more memory than your computer has, and it shouldn't get more than about half.

• Windows: open Settings, choose System, then About. Under Device specifications you'll see how much RAM is installed. Task Manager's Performance tab, under Memory, shows it too.
• Mac: open the Apple menu and choose About This Mac. The Memory line shows the total.

Most launchers ask in megabytes (MB), not gigabytes. These are the numbers to type:

CurseForge app

The CurseForge app has one setting for every pack, and an override for each profile.

For every pack:

1. Click the settings cog in the bottom-left corner of the app.
2. Under Game Specific, choose Minecraft.
3. Scroll down to Java Settings and move the Allocated Memory slider.

For one pack only:

1. Go to My Modpacks and open the pack.
2. Click the three-dot menu next to Play and choose Profile Options.
3. Turn off the option to use the system memory settings, move the slider, then click Done.

The per-pack value wins over the global one, so if a pack ignores your new global setting, check its profile options.

Modrinth App

For one instance:

1. Open the instance and click its settings.
2. Go to the Java and memory tab.
3. Switch on Custom memory allocation and drag the slider.

For every instance: open the app's settings (the cog), find Java and memory under Instance defaults, and set Memory allocation. Instances use this unless they have their own custom allocation.

Prism Launcher

For one instance:

1. Select the instance and click Edit.
2. Choose Settings, then the Java tab.
3. Tick the Memory box. The instance now uses its own values instead of the global ones.
4. Set Maximum Memory Usage.

For every instance: open Prism's own settings, go to the Java tab and set the maximum in the Memory section. Any instance with its Memory box unticked follows this.

Prism shows a warning under the value if it's close to, or more than, your computer's memory.

ATLauncher

For every instance: click Settings in the sidebar, open the Java/Minecraft tab and set Maximum Memory/Ram.

For one instance: go to Instances, click Settings on the instance you want, open its Java/Minecraft tab, set the maximum memory and click Save.

Official Minecraft Launcher

The official launcher has no slider. You change a Java argument instead.

1. Open the Installations tab.
2. Hover over the installation you play (for a modded game, the NeoForge or Forge one), click the ⋯ button and choose Edit.
3. Open More options.
4. In JVM arguments, find -Xmx2G at the start. Change the number: -Xmx4G for 4 GB, -Xmx6G for 6 GB.
5. Click Save.

Change only the -Xmx value. The G means gigabytes; leave the rest of the line as it is. If you break the line, a fresh installation brings back the default.

How much to give

Short version: about 4 GB for a small pack, 6 GB for a medium one, 8 GB for a large one, and never more than about half your computer's RAM. More than a pack needs can make stutters worse, not better. The full reasoning, and how to tell whether memory is really your problem, is in how much RAM to allocate for a modpack.

Let the pack tell you the number

Most people guess, then guess again after a crash. Packspire builds NeoForge 1.21.1 packs and tests each one on a real server and a real game client, measuring memory as it goes, so the pack's page says how much to set in your launcher and how much a server needs.

Plan your pack with Packspire. If more memory didn't fix your crash, see how to find the mod causing a crash.

Frequently asked questions

How do I allocate more RAM to Minecraft in CurseForge?

Click the settings cog, choose Minecraft under Game Specific, and move the Allocated Memory slider under Java Settings. To change one pack only, use Profile Options from the three-dot menu next to Play.

How do I give Minecraft more RAM without a mod launcher?

In the official Minecraft Launcher, edit the installation, open More options and change -Xmx2G in the JVM arguments to a bigger number, such as -Xmx4G.

Why didn't my new RAM setting do anything?

The game reads the setting when it starts, so close and relaunch it. If it still uses the old amount, the instance or profile probably has its own memory override, which wins over the launcher's global setting.

Can I give Minecraft too much RAM?

Yes. Giving it more than about half your computer's memory starves everything else, and a very large allocation can make Java's occasional memory clean-ups longer, which shows up as stutters.

Sources

• Allocating memory, the Enigmatica modpack team's guide to the CurseForge app settings
• Modrinth App source code, for the instance settings tabs
• Prism Launcher: Java settings
• ATLauncher source code, for the Java/Minecraft settings tab
• Minecraft Launcher and Launcher 2.1.367x, on the Minecraft Wiki, for JVM arguments and the 2 GB default
• Which version of Windows am I running?, Microsoft, for finding installed RAM
• Get system information about your Mac, Apple