Virtualization Ratio Calculator

Measure the three ratios that describe a virtual estate: VMs per host, vCPU per core and allocated versus physical memory.

About Virtualization Ratio Calculator

Three ratios describe an estate and they fail differently. VMs per host is a commercial number, vCPU per core is a scheduling number that only hurts once ready time rises, and the memory ratio is the hard one — above 1.0 the hypervisor is reclaiming, and beyond about 1.4 it is usually swapping. These are the numbers reported to management and used in licence negotiations, and each has a different failure mode — quoting only VMs per host hides whether the estate is one workload spike away from memory contention.

Formula

Virtualization Ratio

VMs per host = VMs ÷ hosts; vCPU per core = allocated vCPUs ÷ physical cores; memory ratio = allocated VM memory ÷ physical memory. The density score weights those 40/30/30 against healthy bands.

vCPU per core: Healthy band is roughly 2:1 to 5:1 for general-purpose workloads
memory ratio: Above 1.0 means overcommit; above 1.4 usually means active reclamation
density score: Composite of density against target plus CPU and memory ratio health

Worked example

With the default values below, Virtualization Ratio Calculator returns VMs per Host of 24.0. Change any input above and every figure here is recalculated in your browser.

Inputs used

Hypervisor hostsaccepts 1–5,000 hosts: 10 hosts
Virtual machinesaccepts 1–500,000 VMs: 240 VMs
Total physical coresaccepts 1–500,000 cores: 320 cores
Total vCPUs allocatedaccepts 1–2,000,000 vCPU: 1,120 vCPU
Total physical memoryaccepts 1–5,000,000 GiB: 5,120 GiB
Total memory allocated to VMsaccepts 1–5,000,000 GiB: 4,600 GiB
Target VMs per hostaccepts 1–500 VMs: 25 VMs

Results

VMs per Host: 24.0 VMs
vCPU per Physical Core: 3.50 :1
Allocated to Physical Memory: 0.90 :1
Average vCPUs per VM: 4.67 vCPU
Density Score: 98 / 100
Estate Assessment: Balanced estate — density, CPU and memory ratios are all in healthy ranges

Step by step

1Values used
2Virtualization Ratio
3VMs per Host= 24.0 VMs
4vCPU per Physical Core= 3.50 :1
5Allocated to Physical Memory= 0.90 :1
6Average vCPUs per VM= 4.67 vCPU
7Density Score= 98 / 100
8Estate Assessment= Balanced estate — density, CPU and memory ratios are all in healthy ranges

Assumptions and limits

The result is derived only from the 7 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is Virtualization Ratio calculated?

VMs per host = VMs ÷ hosts; vCPU per core = allocated vCPUs ÷ physical cores; memory ratio = allocated VM memory ÷ physical memory. The density score weights those 40/30/30 against healthy bands. Three ratios describe an estate and they fail differently. VMs per host is a commercial number, vCPU per core is a scheduling number that only hurts once ready time rises, and the memory ratio is the hard one — above 1.0 the hypervisor is reclaiming, and beyond about 1.4 it is usually swapping.

Why does Virtualization Ratio matter?

These are the numbers reported to management and used in licence negotiations, and each has a different failure mode — quoting only VMs per host hides whether the estate is one workload spike away from memory contention.

What values do I need to enter?

This calculator takes 7 inputs: Hypervisor hosts, Virtual machines, Total physical cores, Total vCPUs allocated, Total physical memory, Total memory allocated to VMs, Target VMs per host. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.