Critical Power Calculator
Enter data points of your max efforts for given durations and get your Critical Power curve. After calculation, you can update your profile with new FTP and W' values.
Understanding Critical Power and W'
Critical Power (CP) is the highest power output you can sustain for a prolonged period without continuously accumulating fatigue. In practical terms it sits close to your Functional Threshold Power (FTP), though they are defined differently: FTP is typically the average power you can hold for roughly 40 minutes to one hour, while CP is derived mathematically from the relationship between work done and time to exhaustion across multiple efforts.
W' (pronounced "W prime") represents the finite amount of work you can perform above CP before exhaustion. Think of it as a battery: once you ride above CP you start draining W', and when it runs out you are forced to drop back to or below CP. A larger W' means you can tolerate longer surges or a higher pace above threshold - useful in breakaways, short climbs or the final sprint of a race.
How to Perform the Test
The standard approach is to perform two or three maximal efforts of different durations on separate days (or with enough recovery between them). Common durations are 3 minutes, 7-10 minutes and 15-20 minutes. Each effort should be truly all-out and paced as evenly as possible - going out too hard and fading will skew the result. Record your average power for each effort, enter the duration and power into the calculator, and the tool fits the CP model to your data.
The resulting power-duration curve shows estimated maximum power across a wide range of durations. You can use this curve to set pacing targets for time trials, hill climbs or any effort where you know the approximate duration in advance. If you have a rider profile, saving the calculated FTP and W' values lets other tools on this site - such as the Power - Time Calculator - generate more personalized predictions for your rides.