Proxmox CPU & vCPU Calculator

How many vCPUs can a host provide?

CPU is more forgiving than RAM: virtual machines rarely use all their vCPUs at once, so hosts commonly overcommit CPU several times over. This calculator turns physical cores and threads into an available-vCPU figure at your chosen overcommit ratio, and tells you how many VMs of a given size fit.

The formula

Available vCPUs ≈ (physical cores × threads per core − host reserve) × overcommit ratio. Divide by vCPUs per VM to get VM density. A ratio of 3–4:1 is typical for general VPS workloads; CPU-bound workloads need a lower ratio to avoid steal time.

Watch for CPU steal

Overcommit too aggressively and guests wait for physical cores — visible as CPU steal time inside the VM. If customers report sluggishness under load, lower the ratio or spread VMs across more nodes.

Frequently asked questions

What CPU overcommit ratio is safe on Proxmox?

For general VPS workloads, 3–4 vCPU per physical thread is common. Reduce it for CPU-intensive workloads and watch steal time inside guests.

Do hyper-threads count as cores?

They add capacity but are not full cores. Set threads per core to 2 for hyper-threaded CPUs; the calculator treats them as schedulable threads, not equal to physical cores.

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