By Zencalcy Editorial TeamLast reviewed About us
Estimate your functional threshold power, the highest power you can roughly hold for an hour, from a best 20 minute effort. The common approach takes 95 percent of the 20 minute average. Add your body mass to see the result in watts per kilogram.
Estimate functional threshold power from a 20 minute test.
FTP = 0.95 × best 20 minute average power (W)
The 0.95 factor assumes a well-paced 20 minute test. A test that started too hard or too easy skews the estimate, and FTP itself is really the power you can hold near an hour, not exactly one hour.
| Symbol | Meaning |
|---|---|
| power | Your best sustained 20 minute average power, in watts. |
| body mass | Optional body mass in kilograms, used for the watts per kilogram figure. |
A best 20 minute average of 250 W gives an estimated FTP of 0.95 × 250 = 238 W, which is 3.4 W/kg at 70 kg. A 20 minute best of 300 W gives an FTP of about 285 W.
Functional Threshold Power is the highest power you can hold in a steady state for roughly an hour, and the standard field test estimates it from a hard twenty minute effort. The common convention takes ninety-five percent of your best twenty minute average power, so a twenty minute average of 280 watts implies an FTP near 266 watts.
The five percent discount exists because a twenty minute effort is ridden slightly above true threshold. Holding a fraction more than you could sustain for an hour is possible over twenty minutes, so scaling the shorter effort down approximates the longer one. The factor is a practical convention rather than a precise law of physiology.
FTP anchors training intensity, from easy endurance rides to hard threshold intervals, and it makes power zones portable between riders and between days. It also lets you track fitness across a season, since a rising FTP at the same body weight means more sustainable power.
A single test carries error from pacing, fatigue, and equipment calibration, so repeat it under similar conditions and expect some scatter. A test that starts too hard often undershoots the true twenty minute best, while a well paced effort that finishes strong tends to give a more trustworthy number.
Continue with the Gear Inches Calculator, Power to Weight Calculator, or the Bike Calorie Calculator — or browse more cycling tools and all sports calculators.
Warm up well, ride a hard but even five minute effort, recover briefly, then ride 20 minutes as hard as you can pace evenly. Use the average of those 20 minutes.
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Content updated: September 2026