Critical Swim Speed Calculator
Calculate Critical Swim Speed (CSS) as pace/100 m from two maximal pool efforts over different distances.
Στο προτεινόμενο πρωτόκολλο κολύμπησε πρώτα τα 400 m, κάνε 10–15 λεπτά εύκολη αποκατάσταση και κολύμπησε έπειτα τα 200 m.
400 m 6:20 · 200 m 2:50 · 1:45 /100m
- Speed
- 0.952 m/s
- D′
- 38.1 m
CSS 1:45 /100m
Predicted swim times from CSS
| Distance | Time |
|---|---|
| 200 m | 2:50 |
| 400 m | 6:20 |
| 800 m | 13:20 |
| 1500 m | 25:35 |
How it works
Select your protocol and enter the total time for each effort. For the recommended 200+400 protocol, swim 400 m first, then 200 m, with 10–15 minutes of rest and easy swimming between them. Both efforts should be maximal, with pacing as even as possible. Use the same pool and start type. Repeat tests in the same conditions so results are comparable.
What to keep in mind
Results are affected by protocol distances, pacing, fatigue, stroke, pool length and start type. Results from different protocols or conditions are not directly comparable.
Methodology & sources
CSS uses the two-parameter distance–time model: CSS = (D₂ − D₁) / (T₂ − T₁). The result is converted to pace/100 m without intermediate rounding. D′ is the distance intercept of the same model: D′ = D − CSS × t. It is a model parameter, not a training target. The recommended practical protocol is 200+400. The 400+800 protocol reduces the relative influence of the shorter effort but requires greater endurance, sound pacing and sufficient recovery.
Last updated: 15 June 2026
Use CSS to guide your training
CSS is a useful reference point, but it is not a training plan. Using it well depends on interval duration, recovery, total load and your race goal.
Together we can use your data to organise swim sessions with a clear purpose and appropriate progression.