Free Memory Estimate Calculator

Work out free memory estimate instantly with clear inputs, formula shown and shareable results.

About Free Memory Estimate Calculator

Summing RSS across processes overstates memory use because shared pages — libraries, the binary itself, copy-on-write pages after fork — are counted once per process. Subtracting the shared portion gives a far more realistic figure, which is why PSS or the kernel's own accounting should be used rather than adding up ps output.

Formula

Shared-page adjustment

naive = processes x RSS; actual = processes x (RSS - shared) + shared; double counted = naive - actual

Worked example

With the default values below, Free Memory Estimate Calculator returns Estimated free memory of 22.88. Change any input above and every figure here is recalculated in your browser.

Inputs used

Total RAMminimum 0.1 GB: 32 GB
Application processesminimum 1: 24
Resident memory per processminimum 0.1 MB: 380 MB
Shared pages counted onceminimum 0 MB: 900 MB

Results

Estimated free memory: 22.88 GB
Naive sum of per-process RSS: 9.12 GB
Actual usage after shared pages: 9.12 GB
Memory double counted by summing RSS: 0.00 GB

Step by step

1Values used
2Shared-page adjustment
3Estimated free memory= 22.88 GB
4Naive sum of per-process RSS= 9.12 GB
5Actual usage after shared pages= 9.12 GB
6Memory double counted by summing RSS= 0.00 GB

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 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

What is PSS?

Proportional set size: each shared page is divided among the processes mapping it, so summing PSS across all processes gives a total that does not double count.

Why do forked workers look so expensive?

They share almost all their memory with the parent through copy-on-write, so RSS reports the full amount for each while actual incremental use is small.