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Critical Swim Speed (CSS) Calculator

Estimate your critical swim speed from two time trials to set training paces.

Critical Swim Speed (CSS)

Estimate CSS from 200m and 400m time trials to set training pace.

Understanding the Inputs

Ensure consistent pacing and full recovery between trials

  • 200m time: Enter minutes and seconds for an all-out 200m swim.
  • 400m time: Enter minutes and seconds for an all-out 400m swim (same session, paced well).

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Complete Guide: Training with CSS

CSS sets provide sustainable threshold work that builds aerobic endurance and technique under moderate fatigue. Keep rest short, volume appropriate, and technique crisp. Retest regularly to keep paces aligned with your fitness.

Frequently Asked Questions

Detailed, SEO-oriented answers

What is Critical Swim Speed (CSS)?

CSS is the theoretical speed you can sustain continuously without exhaustion. It is often used to set aerobic training paces in swimming.

How is CSS calculated?

CSS ≈ (T400 − T200) / 200, yielding a pace per meter. We present pace per 100m and an equivalent speed in m/s.

Why use both 200m and 400m?

Using two distances helps estimate a sustainable threshold pace rather than maximal sprint speed.

How accurate is CSS?

It is a field estimate; pool conditions, pacing, and technique affect results. Keep test conditions consistent.

What rest should I use between trials?

Allow full recovery (e.g., 10–15 minutes easy swimming) between the 400m and 200m efforts in the same session.

How often should I re-test?

Every 6–8 weeks or after a training block that targets threshold improvements.

Does stroke type matter?

CSS is typically assessed with freestyle, but you can adapt testing for other strokes with consistent protocol.

How do I convert CSS to training sets?

Use CSS for aerobic intervals (e.g., 100m repeats at CSS with short rest) and threshold work (e.g., 200m repeats near CSS).

Can I use yards instead of meters?

Yes, but the formula and outputs then apply to yards. This calculator assumes meters. Convert times accordingly.

What if my 200m is not faster than half my 400m?

Re-test with better pacing. The 200m time should be faster; otherwise the CSS estimate will be skewed.

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Critical Swim Speed (CSS) Calculator

Estimate your critical swim speed from two time trials to set training paces.

How to use Critical Swim Speed (CSS) Calculator

Step-by-step guide to using the Critical Swim Speed (CSS) Calculator:

  1. Enter your values. Input the required values in the calculator form
  2. Calculate. The calculator will automatically compute and display your results
  3. Review results. Review the calculated results and any additional information provided

Frequently asked questions

How do I use the Critical Swim Speed (CSS) Calculator?

Simply enter your values in the input fields and the calculator will automatically compute the results. The Critical Swim Speed (CSS) Calculator is designed to be user-friendly and provide instant calculations.

Is the Critical Swim Speed (CSS) Calculator free to use?

Yes, the Critical Swim Speed (CSS) Calculator is completely free to use. No registration or payment is required.

Can I use this calculator on mobile devices?

Yes, the Critical Swim Speed (CSS) Calculator is fully responsive and works perfectly on mobile phones, tablets, and desktop computers.

Are the results from Critical Swim Speed (CSS) Calculator accurate?

Yes, our calculators use standard formulas and are regularly tested for accuracy. However, results should be used for informational purposes and not as a substitute for professional advice.