Swim CSS Calculator
Find your critical swim speed from 400 m and 200 m time trials.
Quick answer: enter your details below and click Calculate CSS — your result appears instantly, right here in your browser. Nothing you enter is uploaded or stored.
S
500 New Tools
Enter your details below.
How to use
- Swim all-out 400 m and 200 m trials on separate days.
- Enter both times in seconds.
- Click Calculate CSS.
About this tool
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.
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.