The Predictive Runner

Critical Power Calculator

Critical Power (CP) is the highest power you can hold in a metabolic steady state — the transition between the heavy and severe intensity domains, above which fatigue turns fast and failure arrives in minutes. W′ is the finite work you can spend above it.

Give it two maximal efforts — one short, one longer — and the two-point model fits both from power = W′·(1/t) + CP. It returns CP and W′, and can optionally check that W′ against Stryd population norms to see whether the test looks typical. Coach Steve Palladino recommends a 3/12 test protocol — a maximal 3-minute effort, then a maximal 12-minute one; see the references below for how to run one.

Type the two efforts yourself, or drop the .fit and we read the measured power instead — Single Activity when both efforts are in one recording, Two Activities when they aren’t.

Have three or more efforts — a race, a hard segment, a separate test day? Use the Multi-Activity CP Calculator, which fits them all by least squares and reports how precisely they pin CP down. Two efforts determine the curve exactly, so that precision only exists from three.

Your CP test

Runs in your browser

A two-effort Critical Power test — a short 3–5 min effort and a longer 10–20 min effort. Enter each effort as its duration and average power.

Short effort

suggest 3–5 min
└ 180 s
Watts

Long effort

suggest 10–20 min
└ 720 s
Watts

Check my W′ against Stryd norms (optional)

The norms come from the SuperPower Calculator.

Nothing here is assumed. We never infer your pod from the file — guessing it wrong shifts the result a whole band.

Compare in
Raw work capacity — no body mass required
Power meter
Stryd only — no norms exist for other meters
Gender
The reference table only has these two rows
kg
Only needed for the J/kg basis

Values are never sent to the server.

Result

217WCritical Power
7.68kJW′
243WEst. 5-min power

Calculate environment adjustment → For a race or a training block in different conditions. This CP is what you produced on test day; the adjustment converts it for another altitude, temperature and humidity.

Power-Duration Curve — power (W) by duration. S 3:00 @ 260 W · L 12:00 @ 228 W.
How CP & W′ are derived — power (W) against 1/time. CP is the intercept and W′ is the slope. S 3:00 @ 260 W · L 12:00 @ 228 W.

References

  1. What is CP / FTP? — By Coach Steve Palladino.
  2. Critical Power and W′ Explained — High North
  3. Protocol for CP Testing — By Coach Steve Palladino. How to run the test: pacing, recovery, choosing a route, and reading the result afterwards.
  4. Palladino Power Project
  5. How does Stryd auto-CP work? — By Coach Steve Palladino.
  6. SuperPower Calculator (SPC) — documentation and the SPCs workbook (opens a copy in your Drive), by Coach Steve Palladino et al. It carries this calculation alongside the rest of its race-planning calculations.