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Azure VM Right-Sizing Calculator

Size an Azure VM down to the vCPU and memory it actually needs from observed peaks plus a headroom target.

Inputs

vCPU
GiB
%

Take the 95th percentile from Azure Monitor over 30 days.

%
%

Leaves headroom for spikes and for a failed instance.

USD
VMs

Recommended vCPUs

4vCPU

Recommended Memory

32GiB

Projected Monthly Cost

$1,680.00

Monthly Saving

$0.00

Saving

0.0%

Recommendation

Correctly sized for the observed peak

Step by step

  1. Values used

    Current vCPUs = 8 vCPU; Current memory = 32 GiB; Observed peak CPU = 22 %; Observed peak memory = 45 %; Target peak utilisation = 70 %; Current monthly cost per VM = 280 USD; VMs in this role = 6 VMs

  2. Azure VM Right-Sizing

    required vCPU = current vCPU × peak CPU% ÷ target utilisation%, rounded up to the next Azure size; memory is checked the same way against the family's GiB-per-vCPU ratio.

  3. Recommended vCPUs

    = 4 vCPU

  4. Recommended Memory

    = 32 GiB

  5. Projected Monthly Cost

    = 1,680.00

  6. Monthly Saving

    = 0.00

  7. Saving

    = 0.0

  8. Recommendation

    = Correctly sized for the observed peak

How it works

Right-sizing converts an observed peak into an absolute resource demand, then divides by the utilisation you are willing to run at to get the size you need. Because Azure sizes come in fixed vCPU steps the answer is rounded up to the next step, and the memory-per-vCPU ratio of the family can force a larger size than CPU alone would. Averages hide spikes, so sizing on the 95th percentile with explicit headroom is the difference between a saving and an outage; validate the projected price against the Azure pricing calculator because cost does not always scale linearly with vCPU across families.

Formula

Azure VM Right-Sizing

required vCPU = current vCPU × peak CPU% ÷ target utilisation%, rounded up to the next Azure size; memory is checked the same way against the family's GiB-per-vCPU ratio.

peak CPU%
95th-percentile CPU from Azure Monitor, not the average
target utilisation%
Peak you are willing to run at, leaving spike headroom
ratio
New vCPU count divided by the current count, used to scale cost

Frequently Asked Questions

How is Azure VM Right-Sizing calculated?

required vCPU = current vCPU × peak CPU% ÷ target utilisation%, rounded up to the next Azure size; memory is checked the same way against the family's GiB-per-vCPU ratio. Right-sizing converts an observed peak into an absolute resource demand, then divides by the utilisation you are willing to run at to get the size you need. Because Azure sizes come in fixed vCPU steps the answer is rounded up to the next step, and the memory-per-vCPU ratio of the family can force a larger size than CPU alone would.

Why does Azure VM Right-Sizing matter?

Averages hide spikes, so sizing on the 95th percentile with explicit headroom is the difference between a saving and an outage; validate the projected price against the Azure pricing calculator because cost does not always scale linearly with vCPU across families.

What values do I need to enter?

This calculator takes 7 inputs: Current vCPUs, Current memory, Observed peak CPU, Observed peak memory, Target peak utilisation, Current monthly cost per VM, VMs in this role. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.

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