// guide

How much RAM does a modded Minecraft server need?

The short answer: 2–3 GB for a small Fabric mod list, about 4 GB for a light modpack, 8 GB for a mid-size pack, and 10–12 GB for the big kitchen-sink packs, with more on top as players spread out. The calculator below works it out for your pack. And past a certain point, RAM isn’t what decides how well the server runs.

Updated October 2026  ·  Java Edition  ·  9 min read

RAM calculator

Pick a pack from our guides, or pick the loader and Minecraft version and enter roughly how many mods the server runs. Then set how many players are online at once. It gives a range: the low end is for players who mostly play near each other, the high end for players who each explore on their own.

The calculator needs JavaScript. The tables below give the same estimates in steps.

How the calculator estimates

It starts from the memory a server needs with its mods loaded and one player online, which grows with the mod count, then adds memory for each extra player, which also grows with pack size. Fabric and Quilt packs count a little lighter, because they split features into many small mods. The Minecraft version sets the Java version. The numbers follow the tables on this page and the RAM advice that pack authors publish, rounded to half a gigabyte. They’re a rule of thumb, not measurements from our hardware, and some packs break the rule: GregTech: New Horizons’ wiki asks for 6 GB plus 0.5 to 1 GB per extra player, more than its 209 mods suggest. Where a pack’s authors give advice, its page in our modpack guides uses it. So when you start from a pack, that page’s pick wins for a group of up to five, and for bigger groups it’s the least we’d suggest. Three packs publish a formula by player count (GregTech: New Horizons, Prominence II and Vault Hunters 3rd Edition); start from one of them and the calculator uses the authors’ formula instead of the mod count, at any group size.

The quick table

Some big packs need less than their mod count suggests because their authors publish lower RAM advice: FTB Skies and FTB StoneBlock 3 have over 200 mods, but FTB’s own launcher setting for each is 6 GB, so we pick 8 GB for a small group. Where a pack’s authors publish RAM advice, the quick picks below take it into account.

DSN’s planned plans follow the same steps: Standard (4 GB, $16/month) for light packs, Premium (8 GB, $30/month) for mid-size packs and Heavy (12 GB, $42/month) for the big kitchen-sink packs with a small group. We’re relaunching on new hardware, so ordering is closed for now: join the launch list to hear when it opens.

Is 4 GB enough?

For a small or light pack, yes. A Fabric list of 30 or so performance and quality-of-life mods, or a light modpack of up to about 80 mods, runs on 4 GB with a handful of players. The official Cobblemon modpack (about 32 mods on Fabric and NeoForge) is a good example: we’d run it on Standard.

For 150 mods or more, no. A mid-size pack needs room for its mods plus every chunk your players load. Squeezed into 4 GB, it either stops with java.lang.OutOfMemoryError or stutters through back-to-back garbage collection. If that’s what you’re seeing, the out-of-memory guide shows how to confirm it.

Remember that 4 GB is for the whole server process, not just Java’s heap: set -Xmx to about 3500M so Java has room for its own overhead. And this page is about the server. The game on each player’s PC needs its own RAM on top.

And 8 GB?

For most modpacks, yes. 8 GB covers mid-size packs of 80 to 180 mods for a group, and many bigger packs whose authors recommend 6 to 8 GB, such as FTB Skies and Create: Arcane Engineering. Some mid-size packs need more than their mod count suggests: Vault Hunters 3rd Edition has 168 mods, but its wiki asks for at least 6 GB plus 2 GB per player on a server, so 8 GB covers only one player. Nor is 8 GB enough for the 300 to 500 mod kitchen-sink packs once a group spreads out: All the Mods 10, Better MC or Prominence II want 12 GB.

RAM for 3, 5 or 10 players

Here’s what the calculator gives for common pack sizes on Minecraft 1.21.1, with the plan it picks. The first number in each cell is for players who stay together, the second for players who spread out.

Pack authors’ advice beats these round numbers: a 200-mod pack built around heavy tech mods can need Heavy for three players, and some 300-mod packs run fine on Premium. Each pack’s page in our modpack guides says which plan we’d pick and why. Bigger groups load more chunks than any formula can guess, so if you run a public server, watch memory in the panel for the first week.

How to allocate more RAM

Where the setting lives depends on how the server starts. In every case, -Xmx sets the most memory Java’s heap may use, and -Xms the amount it starts with.

Forge 1.17+ and NeoForge: user_jvm_args.txt

The installer writes run.bat, run.sh and user_jvm_args.txt next to each other. Both scripts start Java with the arguments in user_jvm_args.txt, so that’s the file to edit; leave the scripts alone. Every line in it starts commented out, ending with:

# A good default for a modded server is 4GB.
# Uncomment the next line to set it.
# -Xmx4G

Remove the # and set your number, for example -Xmx8G, save, then start the server with run.bat on Windows or sh run.sh nogui on Linux and macOS. Our guide to making a modded server walks through the whole file.

Forge 1.16.5 and older, and Fabric: the java command

These start from a jar, so the memory goes in the command itself, usually in a small start.bat or start.sh you keep next to it:

java -Xms8G -Xmx8G -jar <server jar> nogui

Replace <server jar> with the Forge jar the installer created, or the Fabric server launcher jar. A server pack that ships its own start script may read memory from a settings file instead (some use a variables.txt); its readme or the script’s comments say where.

On a hosting panel

A hosting panel starts Java with its own startup command (Pelican and Pterodactyl show it on the Startup tab) and usually sizes the heap from the plan’s memory. If that command doesn’t call run.sh or read user_jvm_args.txt, editing that file changes nothing. The plan’s RAM is a hard ceiling for the whole server process, so on a host, more RAM means a bigger plan. Most hosts let you upgrade in place; check that your world, mods and address carry over before you do.

Whichever way you set it, leave headroom. The JVM uses memory outside the heap too, so keep -Xmx 10–15% under the RAM you have: about -Xmx7000M on 8 GB and -Xmx10500M on 12 GB. On a home PC, leave room for the operating system as well, and for your own game if you play on the same machine.

What actually eats RAM

A Minecraft server keeps every loaded chunk in memory. The three things that decide how many chunks are loaded:

• Player count: each player loads a square of chunks around them. Two players standing together share chunks; two players 10,000 blocks apart don’t.
• View distance: the default of 10 loads 441 chunks per player. Dropping to 8 loads 289. That’s a 35% cut in chunk memory for a difference most players won’t notice. Simulation distance (the part that actually ticks) matters more for CPU than RAM.
• Mods: mods add blocks, entities and registries that live in memory whether anyone’s using them or not. That’s why a 150-mod pack needs more memory than vanilla with only two players online.

World size on disk does not matter for RAM. A 20 GB world with three players uses about the same memory as a fresh one with three players. Generating new chunks does cost CPU, which is why pre-generating the world helps on big packs.

Why CPU matters more than RAM

Once you’ve got enough RAM to hold your chunks, extra RAM does nothing. The server’s main loop (mob AI, redstone, block updates, entity physics) runs on a single thread. That means what decides whether your server hits 20 TPS is the speed of one CPU core, not how many cores or how much memory.

Server CPUs built for lots of small workloads often have many cores and modest clock speeds, which suits running many small servers better than one busy modpack. Desktop-class chips such as the Ryzen 9 7950X, and AMD’s EPYC 4004 server chips built from the same design, boost past 5 GHz, and on a busy modpack that single-core speed shows up directly in TPS. Hosts often run both kinds: Apex Hosting’s own server specs page lists Ryzen 9 7950X nodes next to Xeon Gold 6348 nodes (3.5 GHz at most) in some of the same cities.

When you’re comparing plans, look for the CPU model, and whether the host says which one your server will get. Our comparison of Apex, BisectHosting and Shockbyte lists what each one discloses, with sources.

The JVM flags that matter

If you can edit your server’s startup flags, use Aikar’s flags. They tune the garbage collector so it runs in small frequent passes instead of occasional big freezes. For a 4 GB plan (about 85% of the plan’s RAM for the heap):

-Xms3500M -Xmx3500M -XX:+UseG1GC -XX:+ParallelRefProcEnabled -XX:MaxGCPauseMillis=200 -XX:+UnlockExperimentalVMOptions -XX:+DisableExplicitGC -XX:+AlwaysPreTouch -XX:G1NewSizePercent=30 -XX:G1MaxNewSizePercent=40 -XX:G1HeapRegionSize=8M -XX:G1ReservePercent=20 -XX:G1HeapWastePercent=5 -XX:G1MixedGCCountTarget=4 -XX:InitiatingHeapOccupancyPercent=15 -XX:G1MixedGCLiveThresholdPercent=90 -XX:G1RSetUpdatingPauseTimePercent=5 -XX:SurvivorRatio=32 -XX:+PerfDisableSharedMem -XX:MaxTenuringThreshold=1

Set -Xms and -Xmx to the same value, and leave about 10–15% of your plan’s RAM for the JVM’s own overhead. The plan’s RAM is a hard ceiling for the whole server process, so -Xmx4G with AlwaysPreTouch on a 4 GB plan claims all of it at startup and leaves nothing for Java itself, so the server can be killed or freeze for lack of memory.

Which Java version?

RAM won’t help if the server can’t start. Every Minecraft version needs a specific Java version, and on the wrong one the server stops before the world loads. Match it to the Minecraft version your pack is built for:

Minecraft switched to year-based version numbers in 2026, so 26.1 comes after 1.21.11, and it’s the first release that needs Java 25. One exception to the table: GregTech: New Horizons runs on Minecraft 1.7.10 but ships a server build for Java 17 to 25. The full Minecraft Java version chart lists the Java for every pack we cover. Server stopped with a Java error? See wrong Java version.

Signs you need more RAM (and signs you don’t)

You need more

• Memory sits above 85–90% at peak and the server crashes with OutOfMemoryError in the log. Paste the log into our crash log analyzer to confirm.
• Long freezes every few minutes that line up with GC spikes in /spark or timings.
• You added a big mod or updated your pack and usage jumped.

You need a better CPU, not more RAM

• TPS drops when more players are online, but memory is fine.
• Lag spikes tied to specific areas (mob farms, redstone, big builds).
• “Can’t keep up! Is the server overloaded?” in the console with memory under 70%.

Quick picks for popular packs

Each pack links to its setup guide, with the Java version it needs and the crashes people hit most. More in the modpack guides, the Cobblemon server guide and the NeoForge server guide. Not on the list? Email us the pack name and player count and we’ll tell you the smallest plan that runs it well.