CSS Swim Calculator
Critical Swim Speed is the swimming equivalent of threshold pace. Swim a 400m and a 200m time trial, enter the times, and get your CSS pace plus training zones built around it.
Your time trials
Swim both efforts all-out, fully rested, on the same session.
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How this calculator works
Critical Swim Speed is calculated as the distance difference divided by the time difference of your two time trials: CSS (m/s) = 200 ÷ (400m time − 200m time). Pace per 100m and training zones are derived from that speed.
Assumptions
- • Both time trials are maximal and fully rested
- • Pool swimming with push-offs
Limitations
- • CSS slightly overestimates true threshold for some swimmers
- • Retest as fitness changes
Who this is for
- • Swimmers and triathletes setting swim training paces
- • Athletes who want a repeatable swim threshold test
Who this is not for
- • Open-water race pace without adjustment
- • Swimmers who cannot complete a maximal 400m and 200m
References
Related Articles
Continue exploring our comprehensive triathlon resources
CSS Swim Calculator FAQ
Scientific References
Validation of critical swim speed as a performance index