What FTP is
Functional Threshold Power (FTP) is the highest power output in watts a cyclist can hold on average for roughly an hour. It is the central reference value in power-meter training, because training intensities, race pacing and progress are almost always expressed relative to FTP.
20-minute test and ramp test
The classic all-out hour cannot be repeated often, so a shorter test became standard: 20 minutes of maximal, even effort after a warm-up, multiplied by 0.95. The formula is FTP = average power over 20 minutes × 0.95.
An alternative without a long hard effort is the ramp test: power rises in fixed steps (usually a fixed wattage increase each minute) until the rider can no longer keep up. TrainerRoad uses the formula FTP = best one-minute power × 0.75 for this test. The ramp test is shorter and easier for many riders to sustain, but is considered somewhat less precise than a genuine sustained test, since it derives FTP from a short maximal value rather than an actual 20-minute effort.
Watts per kilogram and the seven power zones
Watts per kilogram (W/kg) is FTP divided by body weight and makes riders of different sizes comparable, especially on climbs. Entering weight is optional; without it the calculator only shows the watt values.
The seven power zones come from Andrew Coggan and were published in the book "Training and Racing with a Power Meter" by Hunter Allen and Andrew Coggan (VeloPress): active recovery up to 55% FTP, endurance 56 to 75%, tempo 76 to 90%, threshold 91 to 105%, VO2max 106 to 120%, anaerobic capacity 121 to 150%, neuromuscular power above 150%. The calculator converts these percentages to watts automatically.
Worked example and limits
Example: an average power of 250 watts over 20 minutes gives an FTP of 250 × 0.95 = 237.5 watts, rounded to 238 watts. At 75 kg body weight that is 238 / 75 = 3.17 W/kg.
Both test types depend heavily on motivation, pacing and form on the day. A 20-minute effort ridden too conservatively underestimates FTP, while a ramp test started too hard and fading early skews the best one-minute power up or down. For triathletes with a bike leg, the triathlon time calculator gives the total time across all disciplines.
Frequently asked questions
How is FTP calculated from the 20-minute test?
FTP = average power over 20 minutes × 0.95. At 250 watts average, that is 250 × 0.95 = 237.5 watts, rounded to 238 watts.
How is FTP calculated from the ramp test?
FTP = best one-minute power in the test × 0.75. At 320 watts best one-minute power, that is 320 × 0.75 = 240 watts. This is the formula TrainerRoad uses for the ramp test.
What does a W/kg value of 3.17 mean?
With an FTP of 238 watts and a body weight of 75 kg, 238 / 75 = 3.17 W/kg. The value makes riders of different weights comparable, especially on climbs, where power per kilogram decides pace.
Which zone matters for threshold training?
Zone 4 in the Coggan model, 91 to 105% of FTP, is the threshold zone. At an FTP of 238 watts that is 217 to 250 watts. Intervals in this zone train the ability to hold high sustained power for 10 to 30 minutes.