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Process Memory (RSS vs VSZ) Calculator

Work out process memory (rss vs vsz) instantly with clear inputs, formula shown and shareable results.

About Process Memory (RSS vs VSZ) Calculator

VSZ counts the entire virtual address space including memory-mapped files, reserved-but-untouched heap and shared libraries, so it routinely exceeds physical memory and is not a measure of consumption. RSS is what is actually resident, and even that double counts shared pages across processes — so real usage for a worker pool is private memory times count plus shared once.

Formula

Memory accounting

private = RSS - shared; real total = instances x private + shared; naive sum = instances x RSS

Worked example

With the default values below, Process Memory (RSS vs VSZ) Calculator returns Real memory for all instances of 3,700.0. Change any input above and every figure here is recalculated in your browser.

Inputs used

Virtual size (VSZ)minimum 0.1 MB
4,200 MB
Resident set size (RSS)minimum 0.1 MB
620 MB
Shared pages within RSSminimum 0 MB
180 MB
Instances of this processminimum 1
8

Results

Real memory for all instances
3,700.0 MB
Private memory per process
440.0 MB
Naive sum of RSS
4,960.0 MB
VSZ to RSS ratio
6.77 x

Step by step

  1. 1Values used
  2. 2Memory accounting
  3. 3Real memory for all instances= 3,700.0 MB
  4. 4Private memory per process= 440.0 MB
  5. 5Naive sum of RSS= 4,960.0 MB
  6. 6VSZ to RSS ratio= 6.77 x

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

Why is VSZ so large for JVM or Go processes?

Both reserve large virtual address ranges up front for their heaps and arenas. The reservation costs no physical memory until pages are touched.

Which metric should alerting use?

RSS or PSS, and container memory.current where cgroups are in use. VSZ alerts fire constantly and mean nothing.

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