Swim calculator
Critical swim speed calculator
Swim a 400m and a 200m all out, enter both times, and get your threshold pace per 100m — the number every swim training zone is built from.
CSS is the fastest pace you can hold aerobically. It is swimming's equivalent of a runner's threshold pace or a cyclist's FTP. Everything above it accumulates fatigue quickly; everything below it you could keep going.
It comes from two all-out time trials. The extra 200m in the 400 is swum at the fastest speed you can actually sustain, so the difference between the two times is what that speed costs.
- CSS in m/s = (400 − 200) ÷ (400m time − 200m time)
- Pace per 100m = (400m time − 200m time) ÷ 2
A 6:00 400m and a 2:50 200m gives a CSS of 1:35 per 100m.
Every swim, scored like every ride.
Set your critical swim speed once and Shape turns your pool and open water swims into training load, on the same chart as your bike and run.