CSS Calculator (Critical Swim Speed)
Threshold swim pace from 400 m and 200 m time trials — the swimmer's FTP.
The two-distance trick isolates the aerobic component: the 200's anaerobic contribution cancels out, leaving the sustainable slope between them. Swim both TTs in one session (200 first, full recovery), push honestly, then train threshold sets at CSS and endurance at CSS+4–6 s/100m.
Formula
For general information only — not medical or training advice. Estimates vary between individuals; consult a qualified professional before changing your exercise or nutrition routine.
Threshold swim pace from 400 m and 200 m time trials — the swimmer's FTP. The CSS Calculator (Critical Swim Speed) is a free, private css swimming tool — every result computes instantly in your browser with no sign-up and no data upload.
About CSS Calculator (Critical Swim Speed)
The two-distance trick isolates the aerobic component: the 200's anaerobic contribution cancels out, leaving the sustainable slope between them. It applies CSS (m/s) = (400 − 200) ÷ (T400 − T200). Use the CSS Calculator (Critical Swim Speed) to get an instant, clearly-explained result with the working shown step by step — free, private and with the source method cited.
How to use CSS Calculator (Critical Swim Speed)
- 1Enter your details in the CSS Calculator (Critical Swim Speed) input fields above.
- 2The result updates instantly with the working and reference bands shown.
- 3Adjust any value to explore how it changes the outcome — it's free and unlimited.
Why use CSS Calculator (Critical Swim Speed)?
- ✓Instant css swimming result that recomputes as you type — no waiting, no page reloads
- ✓100% client-side: your health data never leaves your browser
- ✓Shows the actual formula and your numbers substituted in, so you can see exactly how the result is reached
- ✓Based on published, citable sources (Wakayoshi K et al., Eur J Appl Physiol 1992 — critical swimming velocity)
- ✓Free forever with no sign-up, account or app install
Frequently asked questions
How does the CSS Calculator (Critical Swim Speed) work?+
The two-distance trick isolates the aerobic component: the 200's anaerobic contribution cancels out, leaving the sustainable slope between them. The calculation uses the formula: CSS (m/s) = (400 − 200) ÷ (T400 − T200). Everything runs instantly in your browser as you type — your inputs are never uploaded.
Is the CSS Calculator (Critical Swim Speed) accurate, and what is it based on?+
The method is traceable to authoritative sources: Wakayoshi K et al., Eur J Appl Physiol 1992 — critical swimming velocity. Results are estimates — individual variation always applies, so treat the output as a well-grounded starting point.
Is the CSS Calculator (Critical Swim Speed) free and private?+
Yes. It's completely free with no sign-up, and all computation happens locally in your browser, so none of your health data ever leaves your device.
Can I use this for medical decisions?+
This tool is for general fitness information only, not medical or training advice. Consult a professional before changing your routine.
What can I use the CSS Calculator (Critical Swim Speed) for?+
It's commonly used for css swimming, critical swim speed, swim threshold pace. Threshold swim pace from 400 m and 200 m time trials — the swimmer's FTP.
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