RSS Calculator
Calculate a process's Resident Set Size and its share of total physical memory.
About RSS Calculator
RSS (Resident Set Size) is the portion of a process's memory that is held in physical RAM — as opposed to swapped out or not yet faulted in. It includes both private pages (unique to the process) and shared pages (shared libraries, mmap'd files shared with other processes). RSS divided by total physical memory gives the process's footprint as a percentage, useful for capacity planning and identifying memory-hungry processes.
Formula
RSS percentage
rss_percent = (RSS_KB / total_physical_KB) × 100
- RSS
- resident set size in KB
- M_{phys}
- total physical memory in KB
Worked example
With the default values below, RSS Calculator returns Resident Set Size of 512.00. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Process RSS (from ps/top)minimum 0 KB
- 524,288 KB
- Total Physical RAMminimum 1 MB
- 16,384 MB
- Shared Memory (SHR from top)minimum 0 KB
- 131,072 KB
Results
- Resident Set Size
- 512.00 MB
- % of Physical RAM
- 3.13%
- Private Memory
- 384.00 MB
- Shared Memory
- 128.00 MB
Step by step
- 1RSS in MB= 512 MB
- 2% of physical RAM= 3.13%
- 3Private (non-shared) memory= 384 MB
Assumptions and limits
- The result is derived only from the 3 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 RSS different from VSZ?
RSS counts only pages actually resident in physical RAM, while VSZ (Virtual Size) counts the entire virtual address space including memory-mapped files, reserved regions, and swapped-out pages — VSZ is always >= RSS.
Can I sum RSS across processes to get total memory usage?
Not accurately — shared pages (libraries like libc) are counted in every process's RSS that maps them, so summing overcounts. Use PSS (Proportional Set Size from /proc/PID/smaps) for accurate per-process accounting.