Tools / Minecraft
Minecraft Server RAM & JVM Flags Calculator
Pick your player count and server type and get a recommended -Xmx plus a ready-to-paste startup command. Modern JVM defaults first, which is what Paper now recommends on a current Java runtime, with Aikar's tuned G1 flags beside it for when you actually have GC pauses to fix. Runs in your browser.
Recommended allocation: 6 GB
Start here (modern JVM defaults, Java 25):
Only if you see GC pauses (Aikar's tuned G1, ):
Want this on a real server? Supercraft hosts Minecraft →
How the estimate works
RAM scales with what the server has to keep loaded: the world, the render/view distance, your plugins or mods, and the number of players. The calculator starts from a base for your server type, adds a per-player amount, and bumps it for a high view distance, then rounds to a sensible heap size. Treat it as a strong starting point, then watch your server's actual memory and timings and adjust.
The first command is just a heap size on a modern JVM, which is where Paper now tells you to
start: run it, watch your tick time, and tune only against a problem you can see. The second is
Aikar's flags, tuned G1 settings that keep pause times low by collecting in small
steady increments, with -Xms equal to -Xmx and AlwaysPreTouch
so the heap is reserved up front; at 12GB and above it switches to the large-heap variant
automatically. They are worth reaching for on a big heap or a heavy pack, and are cargo cult on a
small one.
Leave room outside the heap. The JVM's own overhead, native memory and the
operating system live outside -Xmx, and Paper puts that at roughly 1 to 1.5 GB. That
is a better rule than a flat percentage: on a small box it works out near the old 75% advice, and
on a large one that advice reserves far more than anything needs.
Java version. Minecraft 26.1 and later require Java 25, and raised the default allocation from 2 GB to 4 GB. Versions up to 1.21.11 run on Java 21. Running 26.x on Java 21 fails at startup rather than degrading.
Right-sizing a server you actually rent?
Picking a plan is exactly this calculation - RAM for the world, the mods, and the players. The tool is free and needs no account; if you want a host where the plan tiers line up with these numbers, Supercraft is one option among many. See also our modpack sizing guide.