Perform a 3-minute maximal effort. Record the average power for the full test and the average power of the final 30 seconds.
Critical Power
280W
Modelled severe-intensity boundary
W' (Work Above CP)
30.6kJ
Finite modelled work term above CP
Time: 7:17
| Zone | Power (W) | % CP | Description |
|---|---|---|---|
Zone 1: Active Recovery | 0 - 154 | <55% | Very easy spinning, recovery rides |
Zone 2: Endurance | 155 - 210 | 55-75% | All-day pace, fat burning, base building |
Zone 3: Tempo | 211 - 252 | 75-90% | Moderate effort, sustainable for hours |
Zone 4: Threshold | 253 - 294 | 90-105% | Hard effort at or near CP |
Zone 5: VO2 Max | 295 - 336 | 105-120% | Very hard, 3-8 minute efforts |
Zone 6: Anaerobic | 337 - 420 | 120-150% | Maximal efforts, 30s-3min |
Zone 7: Neuromuscular | 421 - MAX | >150% | Sprint power, <30 seconds |
Estimate Critical Power (CP) and W' with a 3-minute all-out, two-point, or three-point power-duration model. Invalid nonpositive fits are rejected; zones and time-to-exhaustion values remain model estimates.
Critical Power represents the model's severe-intensity boundary, while W′ represents a finite amount of work available above CP. The calculator fits those parameters from a 3-minute all-out test or from two or three maximal power-duration efforts.
The two-point method uses maximal 3- and 12-minute powers. The three-point method uses 1-, 5-, and 20-minute powers. Those efforts should be recent, well paced, and performed with enough recovery that each reflects maximal capacity.
For the 3-minute all-out method, the final 30-second average estimates CP and the difference between full-test average power and CP estimates work above CP. Peak 30-second power is not a substitute for full-test average power.
The work-time form is total work = W′ + CP × time. Above CP, modeled time to exhaustion is W′ divided by the difference between target power and CP. At or below CP the two-parameter equation does not provide a finite exhaustion time.
A fitted CP is not guaranteed to equal FTP, and W′ is not a direct measurement of one physiological energy store. Both depend on protocol, effort quality, and model choice.
Non-descending test powers, CP below the supported 50-watt boundary, or nonpositive W′ indicate that the entered efforts do not produce a usable fit. Recheck units, durations, fatigue, and whether each effort was truly maximal.
The displayed CP percentage zones are transparent planning bands, not standardized research-derived CP domains. Use them as a simple interface, not as a universal prescription.
No. They are related threshold concepts derived from different protocols and models. Similar values for one athlete do not make them interchangeable definitions.
Longer maximal efforts should have lower average power, and the fitted intercept and slope must yield positive W′ and a supported CP. Invalid ordering or a nonpositive fit cannot be interpreted safely.
Two efforts produce a simple exact line; three efforts allow a least-squares fit across a wider duration range. The extra point helps only when all efforts are high quality and appropriately recovered.