Critical Speed Calculator for Runners (CS, D′)

Critical speed (CS and D′) calculator for runners

Short answer

Critical speed is the slope of distance against time across two all-out runs: CS = (d₂ − d₁) ÷ (t₂ − t₁). A 1,200 m trial in 4:30 and 3,600 m in 15:00 give 3.81 m/s (4:23 per km) and a D′ of 171 m, the distance you can cover faster than CS before you have to slow.

Last reviewed 28 October 20263 published sourcesNot medical advice

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Critical speed calculator

Use two all-out time trials of different distances that each take 2 to 20 minutes, for example 1,200 m and 3,600 m.

Enter the distance and time of both time trials.

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Critical speed from 1,200 m and 3,600 m time trials
1,200 m	3,600 m	CS pace /km	CS pace /mi
5:30	18:00	5:13	8:23
5:00	16:30	4:48	7:43
4:30	15:00	4:23	7:02
4:00	13:20	3:53	6:16
3:30	11:40	3:24	5:29

1,200 m

3,600 m

CS pace /km

CS pace /mi

5:30

18:00

5:13

8:23

5:00

16:30

4:48

7:43

4:30

15:00

4:23

7:02

4:00

13:20

3:53

6:16

3:30

11:40

3:24

5:29

Critical speed and D′

The critical power model applies to running too: plotting distance against time for all-out efforts gives a line whose slope is critical speed (m/s) and whose intercept is D′ (m) (Jones & Vanhatalo, 2017). With two trials, CS = (d₂ − d₁) ÷ (t₂ − t₁) and D′ = d₁ − CS × t₁.

From 1,200 m and 3,600 m time trials, the two-point model gave a mean CS of 4.94 m/s, identical to the three-trial fit, with D′ of 127 m against 123 m (Kordi, Menzies & Galbraith, 2019).

In 12 elite men, CS averaged 5.84 m/s and D′ 328 m, and they ran the marathon at 96% of CS on average (Jones & Vanhatalo, 2017). Recreational marathoners averaged about 3.7 m/s and D′ of 136–149 m, and ran the marathon at 84.8% of CS (Smyth & Muniz-Pumares, 2020).

Related tools

Turn a pace into a finish time with the pace calculator, or predict race times from one result with the race time predictor.

Common questions

How do I test my critical speed?

Run two all-out time trials of different lengths that each take about 2 to 20 minutes, on separate days or with full recovery, for example 1,200 m and 3,600 m on a track. Kordi et al. found those two distances gave the same critical speed as a three-trial test.

How does critical speed relate to marathon pace?

Most runners race the marathon a little slower than critical speed. Elite men in Jones and Vanhatalo's review averaged 96% of CS, while recreational runners studied by Smyth and Muniz-Pumares averaged about 85%.

What is a typical D′?

It varies widely. Recreational marathoners averaged about 136–149 m and elite men about 330 m in the published data. A larger D′ means more capacity for surges and a fast finish.

Sources

Figures on this page were checked against these publications on 28 October 2026.

Jones AM, Vanhatalo A. The 'Critical Power' concept: applications to sports performance with a focus on intermittent high-intensity exercise. Sports Medicine. 2017;47(Suppl 1):65–78. doi.org/10.1007/s40279-017-0688-0

Kordi M, Menzies C, Galbraith A. Comparison of critical speed and D′ derived from 2 or 3 maximal tests. International Journal of Sports Physiology and Performance. 2019;14(5):685–688. doi.org/10.1123/ijspp.2017-0809

Smyth B, Muniz-Pumares D. Calculation of critical speed from raw training data in recreational marathon runners. Medicine & Science in Sports & Exercise. 2020;52(12):2637–2645. doi.org/10.1249/MSS.0000000000002412

Critical speed (CS and D′) calculator for runners