Free swim tool
Critical Swim Speed Calculator
Your CSS is the pace you could hold for a hard 1500m, your swimming threshold. It is the single most useful number for pacing races and setting training that actually works. Two swims and you'll know yours.
How to do the test
- Warm up properly. 400 to 600m easy with a few build efforts, so the test is a true max.
- Swim 400 all-out and record the time.
- Recover fully. 4-5 minutes of total rest.
- Swim 200 all-out and record the time.
- Enter both into the calculator below. Retest every 6 to 8 weeks to track your progress.
Do both efforts in the same session, ideally in a pool with a clock. Pace them evenly rather than sprinting the first length.
Enter your test
Two maximal swims, one honest number.
Maximal effort, mm:ss.
Maximal effort, mm:ss.
Your training paces
Set every swim session off your CSS. These are target paces per 100m, from easy aerobic work up to race speed.
| Zone | Pace | What it's for |
|---|
Predicted race swim ranges
Estimated ranges for your CSS level, accounting for how pace naturally fades as the distance grows, not a flat pace multiplied out. Open water, wetsuit and conditions shift the real number.
Use this in the Weymouth race planner →Don't go it alone.
Your CSS is one number in a much bigger picture. Real progress comes from a coaching team in your corner, mapping and running the whole journey with you: training, strength and conditioning, nutrition and race-day strategy, built around your life and adjusted as you go. Let us get you to the start line ready, and across the finish line in the best possible shape.
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