The number one reason a modded Minecraft server fails on day one is not the pack, the loader or the host — it is memory. Someone buys a 2GB server, points it at a 400-mod pack, watches the console stop at "Preparing spawn area", and blames whoever sold it to them. So here are the real numbers: what the popular packs need on the server side, where those figures come from, and how to pick a size you will not have to change next week.
Server RAM is not client RAM
The RAM a pack lists on its CurseForge or Modrinth page is usually what the client needs — your own game, rendering included. A dedicated server does no rendering, but it holds the whole world for everyone at once: every loaded chunk around every player, every machine, every mob. For a small group the server figure ends up in the same range as the client figure; for a busy server it goes higher.
Two things make modded servers hungrier than vanilla:
- Mod count. Each mod registers blocks, items, recipes and code that stay resident. A 500-mod pack idles at several gigabytes before anyone joins.
- World generation. Modern packs add biomes, structures and dimensions. Generating chunks is a burst of memory and CPU, and it happens every time someone explores somewhere new.
Neither Modrinth nor CurseForge publishes a server requirement, so the numbers below come from pack authors' own published guidance, rounded up rather than down. Recommending too much RAM costs a few dollars a month; recommending too little costs a working server.
RAM by modpack (server-side)
"Minimum" is the point below which the pack will not realistically run — our checkout refuses to sell a plan under it. "Recommended" is where a group of friends plays without watching the memory graph.
For a pack that is not in the table, size by loader: a Forge or NeoForge kitchen-sink pack wants 6GB minimum and 8GB recommended; a Fabric pack 4GB and 6GB. Anything that describes itself as "kitchen sink", "everything" or "heavy" belongs at 10GB or more.
Why the modern kitchen sinks sit at 10–12GB
ATM10 and its Aeronautics spin-off are the reference case. The pack author recommends 10GB server-side as the minimum, and it is not a conservative number: roughly 500 mods on NeoForge, quest-driven progression that ends in weeks of automation, and Create contraptions and Mekanism machines that all queue on the main thread. Undersized ATM10 servers are the single most common "my server keeps crashing" report we see — the server does not crash immediately, it crashes an hour into a session when the garbage collector runs out of room.
DawnCraft is the other pack that punishes small servers, for a different reason: Epic Fight's combat AI and its structure-heavy world generation are CPU and memory intensive at the same time. 10GB is the floor; 12GB is where a party can explore without the server stuttering every time a new structure generates.
The entity-driven packs: Cobblemon and Pixelmon
Pokémon-style packs do not have hundreds of mods, but they spawn creatures everywhere, and every one is an entity with a model, an AI and a position the server tracks. Load scales with how many creatures exist, not how many chunks are loaded. Both run at 6GB for a small group; 8GB is the honest recommendation because a world people have played for a while accumulates a lot of tracked entities. Cobblemon is somewhat lighter than Pixelmon and stays closer to vanilla Minecraft's own performance profile.
The older packs: RLCraft and SkyFactory 4
Minecraft 1.12.2 packs are genuinely lighter than modern ones, whatever their reputation. RLCraft's difficulty is in its mechanics, not its footprint: 4GB runs it, 6GB is comfortable. SkyFactory 4 is a skyblock pack, so there is almost no world generation at all — its load comes from automation late in the game. Start at 4GB and move to 6GB when the factories sprawl.
RAM is half the story: CPU matters too
Minecraft's server tick is mostly single-threaded. Once a pack has enough memory, what decides whether a busy evening feels smooth is how fast the main thread can process a tick: Create contraptions, mob farms, machine networks and chunk generation all queue on it. Symptoms of CPU rather than RAM trouble: constant low-grade stutter for everyone that gets worse as more players spread out, while memory sits well below the ceiling.
This is why our Minecraft plans come in two tiers from 8GB up. The Standard tier at 8GB allocates 300% CPU; the Premium tier at the same 8GB allocates 550%, with unmetered NVMe storage and ten backup slots instead of three. On ATM10 or DawnCraft the Premium tier is the upgrade you feel; on RLCraft it is money you do not need to spend.
Sizing rules that hold up
- Start at the recommended figure, not the minimum. The minimum is for a pack that boots; the recommended is for a pack that stays up.
- Player count matters less than you think. Two players in a year-old automated base cost more than eight players in a fresh world. Size for the world you intend to build.
- Pre-generate chunks. Generating 5–6k blocks around spawn before people explore removes the biggest burst load a modded server has. Pair it with a view distance of 8 or so.
- Leave the JVM flags alone. Modern hosts set the garbage collector for you; hand-tuned flags copied from a 2019 forum post usually make things worse.
- Watch the graph. A server that sits near its memory ceiling for long stretches, saves slowly, or stutters when anyone opens a new area is telling you to go up a tier. On a host that resizes without a reinstall, that is a restart, not a migration.
Our Minecraft server hosting plans run from 2GB to 32GB, and each modpack page above pre-selects the pack and a plan sized to it at checkout. If the pack you want is not listed, the configure page searches Modrinth and CurseForge and applies the same floor. For tuning an existing server, see the Minecraft server performance guide.
Frequently Asked Questions
How much RAM does an ATM10 server need?
10GB is the pack author's server-side minimum and the floor our checkout enforces; 12GB is the recommendation for a group that plays regularly, and 16GB for public or automation-heavy communities. The same figures apply to ATM10 Aeronautics.
Is 4GB enough for a modded Minecraft server?
For a 1.12.2-era pack like RLCraft or SkyFactory 4, yes, with little headroom. For any modern Forge or NeoForge pack, no — the loader and a typical mod list need 6GB before the world loads. Our checkout blocks plans that are too small for the pack you pick.
How much RAM does a Cobblemon or Pixelmon server need?
6GB to start, 8GB recommended. Both are entity-driven: the load grows with the number of creatures in the world rather than the size of the map, so a long-running server drifts upwards over time.
Does more RAM make a laggy server faster?
Only if memory was the problem. If the server has headroom but still stutters when people spread out or machines run, the main thread is the limit, and more CPU allocation (our Premium tier) helps where more RAM will not.
Do I need to install Java for a modpack server?
No. Provisioning installs the Java version the pack's Minecraft version requires — Java 21 for NeoForge 1.21.1, Java 8 for a 1.12.2 pack — along with the loader and the pack itself, before you first join.