Power capacity tool

Critical Power Calculator

Use MMP points to fit CP and W', and derive Pmax and eFTP.

CRITICAL POWER
CP
W
W'
kJ
PMAX
W
eFTP
W

What is Critical Power?

Critical Power (CP) is a modeled sustainable power reference. Work above CP draws from W', so reliable 3-20 minute MMP points usually produce a more useful CP/W' estimate than sprint-only data. Use CP with training load and workout quality before changing zones.

Calculator

Paste your best power (watts) for common durations and choose which points to include.

Inputs
Enter MMP (max mean power) values. Toggle which points are used for CP/W' fitting.
MMP Points
1s MMP (W)
5s MMP (W)
1m MMP (W)
3m MMP (W)
5m MMP (W)
12m MMP (W)
20m MMP (W)
Tip: enable at least two points ≥ 3 minutes for fitting.
Model: linear work-time fit (P·t vs t). CP is the slope and W' is the intercept. Treat results as estimates and validate with repeatable tests.
Results
Select at least two valid points to see results.
Add MMP values (watts) and enable at least two ≥ 3-minute points.
Explained
What these outputs represent in training terms.
CP
Your sustainable power ceiling from the model fit. Used as a reference for long intervals and endurance zones.
W'
Your finite work capacity above CP, expressed as an energy-like number (kJ). It influences repeatability of hard efforts.
Pmax
A practical peak power proxy from your short-duration best power. Useful for sprint/anaerobic context.
eFTP
Estimated FTP from 20-minute power when available, otherwise based on CP.

How to use the Critical Power calculator

1

Collect quality power points

Use recent max mean power values, especially 3-20 minute efforts, recorded with the same power source when possible.

2

Select points and calculate

Toggle the efforts you trust for CP/W' fitting, then review CP, W', Pmax, and eFTP together.

3

Validate before changing zones

Treat the result as a model estimate. Compare it with workouts, repeatable tests, and fatigue before updating training targets.

FAQ

What is Critical Power (CP)?
Critical Power (CP) is a modeled sustainable-power reference from your best mean-max efforts. Work above CP draws from W'. This critical power calculator fits CP from MMP points—usually 3–20 minute efforts—rather than treating a single test as the threshold.
How many MMP points do I need?
You need at least two valid MMP points of about two minutes or longer. Three or more quality points spread across 3–20 minutes usually give a more stable CP and W' fit. Short sprints help Pmax but add noise if you include them in the CP model.
How is CP different from FTP?
CP comes from a model fit across multiple MMP durations. FTP is usually an empirical threshold, such as 95% of a 20-minute effort or a file-based estimate. They can be close, but they are not the same number. Use this page for MMP fitting; use the file-based tool when you have an activity file.
What does W' mean?
W' (W prime) is your finite work capacity above CP, shown as an energy-like value in kJ. Hard efforts above CP spend it; easier riding below CP lets it recover. A larger W' usually means you can repeat more work above CP before fading.
How accurate is this Critical Power calculator?
It is only as good as the MMP points you enter. Mixed power meters, paced-down efforts, or points clustered in one duration can skew CP and W'. Treat CP, W', Pmax, and eFTP as estimates and confirm them with repeatable workouts before changing zones.

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