Proxmox Resource Calculator

Work out how many VMs of a given plan fit on a Proxmox VE host, leaving room for the host, ZFS and growth.

  • Free
  • No Sign-Up
  • Runs in Your Browser

The Host

One VM

CPU Overcommit
Disk Overcommit
Fill in the host and one VM to see how many fit.

How to Use

How to use the Proxmox Resource Calculator

  1. 01

    Describe the host

    Physical cores (threads if hyper-threading counts for you), RAM and usable storage.

  2. 02

    Describe the plan

    vCPU, RAM and disk for one VM, and how far you are willing to overcommit CPU.

  3. 03

    Read the limit

    The smallest of CPU, RAM and disk is how many VMs fit; the limiting resource is highlighted.

Servers & Hosting

About the Proxmox Resource Calculator

What to leave for the host

Proxmox itself needs 2 to 4 GB of RAM, plus more for Ceph (around 4 GB per OSD) if you run it. ZFS uses RAM for its ARC cache: by default up to half the host's memory on older installs, and 10% (capped at 16 GB) on Proxmox VE 8.1 and later. Set zfs_arc_max deliberately, and count it here.

Never plan to 100%. Leave 10 to 15% of RAM free so the host never swaps or calls the OOM killer, which stops whole VMs.

Overcommitting CPU and RAM

CPU overcommits well because most VMs are idle most of the time: 3 to 4 vCPUs per thread is common for general hosting, 1:1 for game or CI servers that run hot. RAM does not overcommit safely on KVM, even with ballooning and KSM, so this calculator counts RAM at 1:1.

Thin-provisioned storage (LVM-thin, ZFS, qcow2) lets you sell more disk than you have, but a full pool pauses every VM on it. Watch real usage, not allocated size.

Host Sizes

32 GB Host64 GB Host128 GB Host256 GB Host512 GB Host1 TB Host

What it can't tell you

  • Disk speed (IOPS) is often the real limit on busy hosts and is not modelled.
  • The figures are a plan, not a guarantee: noisy neighbours and real usage vary.

Frequently asked questions

How many VMs can a Proxmox server run?
It depends on RAM first: divide the RAM left after the host and ZFS reserves by each VM's RAM. A 128 GB host with 16 GB reserved fits about 26 VMs of 4 GB, with some headroom.
What CPU overcommit ratio is safe?
For general VPS hosting, 3:1 to 4:1 vCPUs per thread is common. Use 1:1 or 2:1 for CPU-heavy workloads.
How much RAM does ZFS need on Proxmox?
ZFS works with little RAM, but caches with whatever ARC allows. Proxmox VE 8.1+ defaults to 10% of RAM, up to 16 GB. Set zfs_arc_max in /etc/modprobe.d/zfs.conf to fix it.

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