Why Minecraft Lunar Client needs more RAM and when to increase it

Minecraft Lunar Client runs inside Java, which gets a fixed amount of your computer's RAM when it starts. By default, that amount is usually between 512 MB and 2 GB — enough for vanilla Minecraft on a small world, but not enough if you're running mods, playing on a server with many players, or rendering distant chunks. When Lunar Client runs out of RAM, the game stutters, freezes, or crashes because Java has to constantly clean up memory instead of running the game smoothly.

You can tell Lunar Client needs more RAM when the frame rate drops suddenly during normal play, the game freezes for a few seconds at a time, or you see an error message mentioning "OutOfMemoryError". Increasing the RAM allocation fixes these problems by giving Java more working space before it has to pause and clean up.

How much RAM to allocate depends on what you're running. Vanilla Minecraft with no mods runs fine on 2 to 4 GB. If you're using a modpack or heavy shader mods, allocate 6 to 8 GB. If your computer has 16 GB of total RAM or more, you can safely give Minecraft 8 to 10 GB without slowing down the rest of your system. Never allocate more than half your total RAM to Minecraft — your operating system and other programs need the rest.

Key Takeaways

  • Open Lunar Client, click the settings gear icon, find the Java Settings tab, and look for the field labeled "Memory" or "RAM Allocation".
  • Enter a number in gigabytes (GB) — start with 4 GB if you have 8 GB of total RAM, or 8 GB if you have 16 GB or more.
  • Close and reopen Lunar Client completely for the change to take effect; restarting the game alone will not explore the new setting.
  • If Lunar Client crashes when ready after changing RAM, you allocated more than your computer has available; reduce the number and try again.
  • Check how much total RAM your computer has before allocating — on Windows, right-click "This PC" and select Properties; on Mac, click the Apple menu and choose "About This Mac".

Finding the RAM setting in Lunar Client

Open Lunar Client and look for the settings icon — it's a small gear or cog symbol, usually in the bottom left corner of the launcher window. Click it to open the settings menu.

In the settings menu, find the tab labeled "Java Settings" or sometimes just "Settings". This is where Lunar Client stores options for how Java runs. Scroll down until you see a field for memory, RAM allocation, or JVM arguments. The label might say "Memory", "RAM", "Max Memory", or "-Xmx" (the technical name Java uses). This is the field you need to change.

If you see multiple memory fields, you're looking for the one that controls the maximum amount of RAM Java can use. It usually has a number followed by "GB" or "M" (for megabytes). Write down what it currently says before you change it — if something goes wrong, you'll want to know what the original setting was.

Changing the RAM allocation

Click in the memory field and clear the current number. Type a new number representing gigabytes of RAM. If your computer has 8 GB of total RAM, enter 4. If it has 16 GB, enter 6 to 8. If it has 32 GB or more, you can go up to 10 or 12, but start lower and increase only if you still see stuttering.

Do not enter a decimal point or a letter — just the number. Lunar Client expects a whole number like 4, 6, or 8, not 4.5 or "4GB". If the field shows a number followed by "M" (megabytes), multiply your intended GB by 1024. For example, 4 GB equals 4096 MB.

After you enter the new number, look for a Save or explore button. Some versions of Lunar Client save automatically when you click away from the field. Others require you to click a button at the bottom of the settings window. Check whether the setting was saved — close the settings menu and reopen it to confirm the number you entered is still there.

Restarting Lunar Client to explore the change

Close Lunar Client completely — not just the game window, but the entire launcher. On Windows, click the X button in the top right corner of the Lunar Client window. On Mac, click the red circle in the top left corner. Wait a few seconds to make sure the program has fully shut down.

Reopen Lunar Client by clicking its icon on your desktop or in your applications folder. The launcher will start fresh with the new RAM allocation. You do not need to restart your computer — closing and reopening Lunar Client is enough.

Start a world or join a server to test whether the change worked. The game should feel smoother, with fewer freezes or frame rate drops. If it still stutters, you may need to allocate more RAM, or the problem may be something else (like your graphics card or internet connection).

What to do if Lunar Client crashes after changing RAM

If Lunar Client crashes when ready when you try to start a world, you likely allocated more RAM than your computer actually has available. This happens most often when someone allocates 16 GB on a computer with only 8 GB total, or when other programs are already using most of the RAM.

Open Lunar Client again and return to the Java Settings. Reduce the RAM number by half — if you set it to 8 GB, change it to 4 GB. Save the setting, close Lunar Client completely, and reopen it. Try starting a world again.

If it still crashes, reduce the number further. Keep reducing until Lunar Client starts without crashing. Once it runs, you've found a safe upper limit. You can then increase it slowly — add 1 GB at a time — until you find the sweet spot where the game runs smoothly without crashing.

Checking your computer's total RAM

On Windows: Right-click on "This PC" or "My Computer" on your desktop or in File Explorer. Select "Properties" from the menu. Look for a line that says "Installed RAM" — this is your total RAM. If you see something like "16.0 GB", your computer has 16 gigabytes.

On Mac: Click the Apple menu in the top left corner and select "About This Mac". A window will open showing "Memory" near the top — this is your total RAM. If it says "16 GB", you have 16 gigabytes available.

Once you know your total RAM, allocate no more than half of it to Minecraft. If you have 8 GB total, allocate 4 GB maximum. If you have 16 GB, allocate 8 GB maximum. This leaves enough RAM for your operating system, web browser, Discord, and other programs you might run while playing.

Frequently Asked Questions

Will giving Minecraft more RAM make it run faster?

More RAM reduces stuttering and freezing, which makes the game feel smoother. It does not increase your frame rate if your graphics card is the bottleneck. If you're already getting 60+ frames per second but the game freezes occasionally, more RAM will fix the freezing. If your frame rate is low overall, the problem is probably your graphics card, not RAM.

Can I allocate all my computer's RAM to Minecraft?

No. Your operating system needs RAM to run, and other programs need RAM too. If you allocate all 16 GB to Minecraft on a 16 GB computer, Windows or Mac will slow to a crawl and may crash. Allocate half your total RAM at most, and less if you run other programs while playing.

What if I don't see a memory field in Java Settings?

Some older versions of Lunar Client hide the memory setting. Try looking for "JVM Arguments" or "Advanced Settings" instead. If you find a field labeled "JVM Arguments", you can add the setting manually by typing -Xmx4G (for 4 GB) or -Xmx8G (for 8 GB) into that field. Make sure there's a space before the dash.

Do I need to change RAM allocation for each modpack?

No. The RAM setting in Lunar Client applies to all worlds and servers you play on. If you switch between a modpack and vanilla Minecraft, the same RAM allocation works for both — though you might want to increase it if the modpack uses many mods and you see stuttering.

Why does Lunar Client use RAM at all if I have a graphics card?

Your graphics card handles drawing to the screen, but Java (the language Minecraft runs on) handles everything else — calculating where blocks are, running mods, managing inventory, handling network traffic. Java needs RAM to store all that information while the game is running. More RAM means Java can keep more information ready without pausing to clean up.