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Health & fitness

Critical Swim Speed calculator

Estimate your CSS training pace per 100 metres or yards from 400 and 200 time trials.

Your result

Complete the fields and calculate.

Calculation method and formula

((60 × 400 time – minutes [min] + 400 time – seconds [Sek.]) − (60 × 200 time – minutes [min] + 200 time – seconds [Sek.])) ÷ 2

Understand the inputs

Distance unit
Choose the matching option; it determines the table value or calculation variant.
400 time – minutes
Unit: Min.. Minimum 0. Whole number.
400 time – seconds
Unit: Sek.. Minimum 0. Maximum 59.9. Use a measured value or your own assumption.
200 time – minutes
Unit: Min.. Minimum 0. Whole number.
200 time – seconds
Unit: Sek.. Minimum 0. Maximum 59.9. Use a measured value or your own assumption.

Assumptions and limitations

CSS uses comparable 400- and 200-distance tests in the same unit. Their time difference is halved. Inconsistent timings distort the result; it is not a directly measured threshold.

The formula uses the specified units. Displayed numbers are rounded; whole packs, item counts and full time periods may also be rounded within the calculation.

Worked example

Illustrative values. Replace them with your own inputs for your calculation.

Distance unit
Metres
400 time – minutes
5 min
400 time – seconds
5 Sek.
200 time – minutes
2 min
200 time – seconds
25 Sek.
Example result1:20 /100 m

Formula: (400 time − 200 time) ÷ 2. Use the value as a training pace guide.

Model revision: October 17, 2026 · How CleverCalc works

FAQ

Frequently asked questions

How does Critical Swim Speed calculator work?+

((60 × 400 time – minutes [min] + 400 time – seconds [Sek.]) − (60 × 200 time – minutes [min] + 200 time – seconds [Sek.])) ÷ 2. CSS uses comparable 400- and 200-distance tests in the same unit. Their time difference is halved. Inconsistent timings distort the result; it is not a directly measured threshold.

What assumptions should I consider for this result?+

CSS uses comparable 400- and 200-distance tests in the same unit. Their time difference is halved. Inconsistent timings distort the result; it is not a directly measured threshold. The formula uses the specified units. Displayed numbers are rounded; whole packs, item counts and full time periods may also be rounded within the calculation.

How accurate is the result?+

The formula uses the specified units. Displayed numbers are rounded; whole packs, item counts and full time periods may also be rounded within the calculation. Prices, measurements and model assumptions determine how well the result represents your situation.

Is this calculator free?+

Yes. Calculations and PDF export work without an account or registration.

What happens to my inputs?+

Calculations run in your browser. Results are saved locally only when you add them to My results; favourites and history are also local. Shared links contain your values. The currency tool requests the selected currencies from its rate provider without sending your amount.

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