Cluster Autoscaler Sizing Calculator

Work out cluster autoscaler sizing instantly with clear inputs, formula shown and shareable results.

About Cluster Autoscaler Sizing Calculator

The cluster autoscaler adds nodes when pods cannot be scheduled, so node count is total requests divided by allocatable capacity — not by nominal instance size, since the kubelet, system daemons and eviction thresholds reserve a meaningful share. Reserving 15 percent for bin-packing inefficiency and adding one spare node covers the common case of a large pod that cannot fit anywhere.

Formula

Node count

CPU nodes = ceil(total CPU requests / (allocatable CPU x 0.85)); memory nodes = same for memory; nodes = max + 1 spare

Worked example

With the default values below, Cluster Autoscaler Sizing Calculator returns Nodes required including one spare of 9. Change any input above and every figure here is recalculated in your browser.

Inputs used

Total pod CPU requestsminimum 1 m: 48,000 m
Total pod memory requestsminimum 0.1 GB: 180 GB
Allocatable CPU per nodeminimum 1 m: 7,800 m
Allocatable memory per nodeminimum 0.1 GB: 30 GB

Results

Nodes required including one spare: 9
Nodes needed for CPU requests: 8
Nodes needed for memory requests: 8
CPU capacity unallocated: 23.1%

Step by step

1Values used
2Node count
3Nodes required including one spare= 9
4Nodes needed for CPU requests= 8
5Nodes needed for memory requests= 8
6CPU capacity unallocated= 23.1

Assumptions and limits

The result is derived only from the 4 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 1 decimal place, 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

Why is allocatable capacity less than the instance size?

The kubelet reserves memory and CPU for system daemons and eviction thresholds, typically 5 to 15 percent depending on instance size and configuration.

What causes bin-packing waste?

Pods that do not divide evenly into node capacity. A pod requesting slightly over half a node's CPU leaves the remainder unusable for another copy of itself.