Health & Fitness
Critical Swim Speed (CSS) Calculator
Calculate sustainable swimming pace per 100 metres from timed 400 m and 200 m efforts.
Preparing your result…
What this calculator does
Calculates Critical Swim Speed (CSS) Calculator using the formula verified against the cited source.
What your result means
An estimate from the inputs you enter, within the scope stated below — not advice.
Formula
CSS seconds per metre = (400 m time − 200 m time) ÷ 200
The step-by-step working for your own numbers appears with the result above and in the PDF report.
Frequently asked questions
Symbols and assumptions
- Inputs
- The values entered in the fields above
- • Two-point 200 m/400 m critical-speed estimate: speed=200/(t400−t200) m/s; pace seconds/metre=(t400−t200)/200; pace per 100 m=(t400−t200)/2. Times must be seconds from comparable maximal trials.
Sources and review
Reviewed 2026-10-18 · Next review 2027-04-18
- • Critical speed is derived from the slope of a distance–time relation; the two-trial estimate is protocol-dependent. Require t400>t200>0. It is not a promise of an indefinitely sustainable pace or identical threshold in every swimmer.
Important limitation
This is an educational estimate based only on the values and formula shown. Verify current rates, rules, units, and professional standards before relying on the result. It is not personalized financial or investment advice.
Quick reference
| Scenario | 400 m time (seconds) | 200 m time (seconds) | Critical swim pace per 100 m |
|---|---|---|---|
| Worked example | 420 | 195 | 1:53 |
| Half the amounts | 210 | 98 | 0:56 |
| Double the amounts | 840 | 390 | 3:45 |
Need the full picture? Get the detailed PDF report with charts, tables, formulas and working steps.
Reviewed 2026-10-18 · Next review 2027-04-18
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