CSS swimming calculator
Determine your critical swim speed from a 400 m and 200 m test. You get threshold pace per 100 m and ready-made swim zones.
Everything is computed in your browser — the values you enter are never sent or stored.
Result
- CSS — threshold pace
- 1:53 / 100 m
- CSS — speed
- 0.889 m/s
| Zone | Pace / 100 m | Use |
|---|---|---|
| Z1 | > 2:21 | technika, regeneracja |
| Z2 | 2:05-2:21 | baza |
| Z3 | 1:55-2:05 | tempo |
| Z4 | 1:47-1:55 | okolice progu |
| Z5 | < 1:47 | mocne odcinki |
Swim measurement has real limitations: turns, stroke and watch accuracy all shift the result. Do the test after a warm-up, both distances on the same day.
How we calculate this
- CSS [s/100 m] = (T400 − T200) / 2
- CSS [m/s] = 200 / (T400 − T200)
- Zones: Z1 < 80%, Z2 80-90%, Z3 90-98%, Z4 98-105%, Z5 > 105% CSS
The formulas come from the app’s domain specification and are covered by unit tests. The same code powers zones inside the app.
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In the dashboard you can log workouts and use the training plan included in your tier. New account registration is currently closed.
This calculator is informational and does not replace a doctor, physiotherapist or coach. Results based on population formulas are estimates, not measurements. Read the full disclaimer →