How much RAM does a Minecraft server need?

Every Cobbly free server has 3 GB of RAM, and it is fixed — there is no slider. The question that matters is whether 3 GB is enough for what you want to run, and for most friend-group servers it is. This guide explains where that memory goes, what fits, and what to do when it does not.

What “3 GB” means on a free server

A Minecraft server is a Java program, and Java splits its memory in two. The heap is where the game keeps the world, players, entities and mod data — that is the number people mean when they say a server “has” so much RAM. Around it, Java needs room for its own machinery: loaded code, thread stacks and native buffers.

On Cobbly the 3 GB is the hard ceiling for the whole server, and the heap is set to about 2.4 GB of it (80%). The rest is the headroom Java needs outside the heap. Setting the heap to the full 3 GB would not give you more usable memory — it would just let the server run out of room for everything else and be stopped.

Each free server also gets up to 2 CPU cores. Memory is rarely the first thing that runs out on a small server; tick time usually is. See Why is my Minecraft server lagging?.

A rough guide

• Vanilla or Paper, up to ~5 players — 1.5 to 2 GB is plenty. You have room to spare.
• Paper or Purpur with a handful of plugins, up to 10 players — 2 to 3 GB. Comfortable.
• Fabric with performance and quality-of-life mods — fits easily. Fabric itself is light.
• A small or medium Forge / NeoForge modpack (up to ~100 mods) — 2.5 to 3 GB. Fits, but keep an eye on it.
• A large modpack (150+ mods) — 4 GB and up, often 6 GB. This is more than the free tier gives you.

Every Cobbly server is capped at 10 players online at once, so the player count is rarely what tips a server over — mods and loaded chunks are.

What actually uses memory

• Loaded chunks — the world around each online player is held in memory. Five players building together load far fewer chunks than five players exploring in different directions.
• View and simulation distance — the biggest lever of all. Each step up adds a ring of chunks around every player. Free servers run both at 6, which is why a 3 GB server copes with more than you might expect.
• Entities — dropped items, mob farms, villager halls and big animal pens all live in memory and are updated every tick.
• Mods and plugins — a mod that adds a few blocks is cheap; world-generation overhauls, map renderers and large tech mods are not. Modpacks also load every mod’s code and recipes at startup, before anyone joins.

How to tell if you are running out

You do not need a profiler to spot a server that is short of memory. The signs in the Console tab are:

• java.lang.OutOfMemoryError in the log — the clearest signal there is. The heap filled up.
• The server stopping without a crash report shortly after a lot of players join or a big area loads.
• Long pauses (rubber-banding for everyone at once) that line up with garbage-collection messages in the log.

If you see these on a modpack, it is the pack; if you see them on Paper with a few plugins, look at entities and farms first.

Getting the most out of 3 GB

• Pre-generate the area people will play in (a plugin or mod such as Chunky does this) so terrain is not being created while everyone is online.
• Keep item farms and mob grinders collecting into hoppers or chests rather than leaving thousands of items on the ground.
• Switch redstone clocks and big farms off when nobody needs them.
• On a modpack, remove mods you are not using — every one costs a little, at startup and while running.
• On Vanilla, switching to Paper (for plugins) or adding performance mods on Fabric gets more out of the same memory.

When you genuinely need more

If your pack needs 6 GB, no amount of tuning fixes that on a 3 GB server. One click on the panel clones your world and settings into a paid Spawnly server with more memory and no sleeping, and your free server keeps running so the move is reversible. The other limits — storage, player slots, server count — are covered in What are the limits?.