Proxmox RAM Calculator
Size the physical memory your Proxmox host needs for a set of VMs, including host reserve and overcommit.
How much RAM does a Proxmox host need?
Physical memory is usually the first ceiling you hit on a Proxmox node. You need enough for every VM plus a reserve for the host itself — the kernel, Proxmox services and, if you use it, ZFS ARC. Unlike CPU, RAM overcommit is risky: this calculator lets you model it, but plan conservatively.
The formula
Physical RAM ≈ (number of VMs × RAM per VM ÷ overcommit ratio) + host reserve. An overcommit ratio of 1 means no overcommit (safest). Above 1 assumes ballooning or KSM reclaim some memory — only reliable if guests do not all use their full allocation at once.
Leave a reserve
Always reserve memory for the host. A common starting point is a few gigabytes plus roughly 1 GB per TB of ZFS storage if you run ZFS. Running a host to its memory limit invites the out-of-memory killer.
Frequently asked questions
Should I overcommit RAM on Proxmox?
Cautiously. Overcommit only works if guests do not all use their full RAM simultaneously. Keep the ratio at 1 for critical workloads and rely on ballooning/KSM only where you can tolerate pressure.
How much should I reserve for the host?
A few gigabytes for the host and services, plus extra for ZFS ARC if used. Set it in the calculator to see the impact.
Related
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