Critical swim speed calculator
Threshold pace from a 400 m and a 200 m time trial, then a predicted swim time for sprint, Olympic, half Ironman and Ironman. A guide for the swim, not a lab test.
Swim a 400 m time trial and a 200 m time trial, with plenty of rest between them. Use the same pool and the same stroke, and swim each one as hard as you can hold for that distance.
How the estimate is made
Two time trials
The estimate uses a 400 m and a 200 m, swum hard, with plenty of rest between them. A tired second swim, or a different pool, moves the pace more than a real change in fitness.
The middle 200 m
Take the 400 m time and subtract the 200 m time. What is left is the time for the other 200 m. That pace is critical swim speed: roughly the pace you can hold for 1,500 m.
Speed and pace
Metres per second is that 200 m divided by the time difference. The pace per 100 m is the same difference shared across two lengths. Both numbers are the same swim.
What is critical swim speed?
Critical swim speed is an estimate of the fastest pace a swimmer can sustain for an extended period without exhaustion. It is the threshold speed from a 400 m and a 200 m time trial. Training at or near it is how swimmers build aerobic capacity and endurance in the water.
The result is in metres per second and in time per 100 m. That pace is roughly a 1,500 m swim, the standard-distance triathlon.
How to use it
Do the 400 m and the 200 m with plenty of rest between them, so each swim is a real effort. Use the pace for endurance sets: hold it, or sit just either side of it, rather than turning every length into a sprint.
100% of critical swim speed is the 1,500 m time. A sprint is faster, and the longer swims are slower. Open water, sighting and a wetsuit will move the time.
If you have a tempo trainer, the metronome that sits under your swim cap, or smart goggles, set them to this pace for structured workouts.
The calculators are a starting point. Coaching is where the pace turns into the sets you swim.
More from the library: Critical power · VO2max · Event run pace · Calorie needs · Triathlon coaching · Training articles