Swim Pace and Critical Swim Speed (CSS) Calculator
Enter your 400 m and 200 m test times to get your critical swim speed and threshold pace.
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Swim Pace and Critical Swim Speed (CSS) Calculator by TheCalcTools
How the Swim Pace and Critical Swim Speed (CSS) Calculator works
Critical swim speed is the pace you could hold for a long time without tiring quickly, roughly your threshold. It comes from the extra distance you swam (200 m) in the extra time the 400 m took.
Swim the 400 m first, recover fully, then the 200 m, both all-out. Train at CSS pace, a little faster or slower, for structured threshold sets.
The formula
Worked example
Using the default values shown in the calculator:
| 400 m time: minutes | 7 |
|---|---|
| 400 m time: seconds | 0 |
| 200 m time: minutes | 3 |
| 200 m time: seconds | 15 |
| Distance to plan | 1500 m |
- Times: 420 s and 195 s. CSS = 200 ÷ 225 = 0.889 m/s.
- Pace per 100 m = 100 ÷ 0.889 = 112.5 s, or 1:52.
Result:
| CSS pace per 100 m | 1:52 |
|---|---|
| Critical swim speed (m/s) | 0.889 |
| Seconds per 100 m | 112.5 |
| Time for your distance at CSS (minutes) | 28.1 |
Frequently asked questions
Does this work in yards?
Yes. Swim 400 and 200 yards and the result is per 100 yards.
Sources and further reading
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.