Instructions

To determine your critical power and W’, complete 2-3 maximal efforts, each lasting between 3-mins and 20-mins. We recommend 3-mins, 5-6 mins and 12-mins. You should try to pace these with a consistent power, avoiding a hard start or finish for example.
Find your average power for each effort.
Enter your test data into the calculator below. Be sure to enter the test duration in seconds and not minutes.
Your results will then be automatically calculated. There are two sets of results based on whether you completed two or three tests. Make sure you’re looking at the correct section, depending on how many tests you did.
In the Pacing Calculator section, you can generate estimates of the power you can hold over certain durations, and vice versa. This only works reliably for durations between 3-mins and 20-mins.

To learn more about critical power, and in particular how to interpret the results, check our our article here.

Critical Power and W' Calculator

Test 1:

Test 2:

Test 3:

Input your test results in this section. Make sure you enter duration in seconds, and not in minutes!

If you only did two tests, then just enter results for Test 1 and Test 2.

Results - Two Test Solution

Critical Power (W):

Approximate FTP (W):

W' (kJ):

If you did two tests, your results will appear in this section. If you did three tests, you should read the results from the next section ('three test solution')

Results - Three Test Solution

Critical Power (W):

Approximate FTP (W):

W' (kJ):

Goodness of Fit (%):

If you did three tests, you should read your results from this section. We ideally want the 'goodness of fit' to be above 97%, which indicates your test efforts were all well-paced.

Pacing Calculator

Use this section to estimate the power you can hold for a given duration and vice versa. This only works for durations between 3-mins and 20-mins (180-1200 seconds). Make sure you look at the appropriate section (two test solution if you did two tests, and three test solution if you did three tests).

Enter Target Duration (s):

Estimated Power (W) (Two-Test Solution)

Estimated Power (W) (Three-Test Solution)

Enter Target Power (W):

Estimated Duration (s) (Two-Test Solution)

Estimated Duration (s) (Three-Test Solution)

Testing Tips

Keep things consistent. Both our own experience and data from scientific studies shows that the length of the testing intervals can have a notable impact on your CP and W’ estimates. So, if you’re trying to track changes over time, try to keep the length of the test intervals consistent each time you test.
Be cautious when interpreting your results the first two times you determine your CP and W’, as these results will likely be less reliable due to sub-optimal pacing. Research shows that results become more reliable once you’ve completed the testing protocol at least three times.