How it works
distance = CS · time + D′ (CS = (d₂−d₁)/(t₂−t₁), D′ = d₁ − CS·t₁)
This page keeps the calculation centered on one relationship: distance = CS · time + D′ (CS = (d₂−d₁)/(t₂−t₁), D′ = d₁ − CS·t₁). Inputs are normalized before the final display, which keeps mile, kilometer, pace, speed, or zone outputs from drifting because of rounding. Use the number as a consistent model output, then layer in terrain, weather, recovery, and race execution. Keep the fixed reference values in view: 1500 m, 5:00, 3000 m, 11:00, 360, 4.17 m, 4:00, 250 m.
Sources
- Critical power / critical speed model Monod, H., & Scherrer, J. (1965). “The work capacity of a synergic muscular group.” Ergonomics 8, 329–338 — the linear work–time (distance–time) model behind critical speed.
- Critical speed in running Critical speed is the running analogue of critical power: the asymptote of the distance–time relationship, closely tied to the maximal metabolic steady state (≈ threshold).
- D' (anaerobic reserve) D′ is the finite distance that can be covered above critical speed, reflecting anaerobic work capacity.
FAQ
When should I use the critical speed calculator?
Use it when you want a fast planning number before a run, race, workout, or gear decision. It gives you a consistent estimate without asking you to create an account.
What inputs matter most?
The best result comes from honest, current inputs. Recent race times, realistic body measurements, accurate workout data, and the correct unit setting matter more than perfect formatting. Keep the fixed reference values in view: 1200–1500 m, 2400–3000 m.
How should I read the result?
Treat the output as a planning reference, not a promise. Use it to compare options, set a target range, or sanity-check your watch data before making the final call.
Does this work in miles and kilometers?
Yes. PacerRunning is written for US runners first, so miles are easy to use, but metric conversions are kept alongside them where the tool needs both views.
Why might my real-world result differ?
Terrain, wind, heat, sleep, fueling, training fatigue, and measurement error can all move the real outcome away from the estimate. The Critical Speed critical speed calculator cannot see those details.
Can beginners use it?
Yes. You do not need advanced training knowledge. Enter the numbers you know, read the result as a guide, and keep your effort comfortable when you are unsure.
Critical Speed Calculator results are estimates from the entered data and the cited method. They are useful for planning and comparison, but they are not a diagnosis, prescription, guaranteed race result, or substitute for a coach or clinician.