Swim CSS: The One Pace That Sets Your Swim Training
Critical swim speed sits between sprint pace and easy pace, and it anchors most swim sets. Two time trials are all it takes to find it.
What is the Swim CSS Calculator?
Enter your 400 m and 200 m times in seconds. Critical swim speed is the pace you can hold over distance, worked out from the difference between the two trials. It is a useful training pace, not a race prediction, and it needs two honest all-out trials to mean anything.
How to use it
- Swim all-out 400 m and 200 m trials on separate days.
- Enter both times in seconds.
- Click Calculate CSS.
Worked example
With 400 m in 360 seconds and 200 m in 170 seconds, CSS is 200/190 = about 1.05 m/s, or about 95 seconds per 100 m.
What is the CSS for 400 m in 6:00 and 200 m in 2:50?
About 95 seconds per 100 m: 200 metres divided by the 190-second gap between the trials.
Frequently asked questions
Can I use 200 m and 100 m instead?
The formula works with any two distances, but 400 m and 200 m is the standard pairing.
Is CSS my race pace?
Roughly, for longer swims. It is a sustainable training pace rather than a sprint pace.