Published by MetaSys Limited · Page updated · Editorial policy. Educational information; not a medical review.
What FTP Actually Measures
Functional Threshold Power is the highest average power you can hold in a steady, sustainable effort for roughly one hour. It sits right at the boundary between efforts your body can fuel mostly through aerobic metabolism and efforts that force you into rapidly accumulating fatigue. Ride even slightly above FTP and you'll blow up within minutes; ride at or just below it and, with the right pacing, you could hold that output for the better part of an hour. That single number becomes the anchor for almost everything else in structured cycling training — how hard your intervals should be, how your race efforts should be paced, and how your fitness is trending over a season.
Why We Use a 20-Minute Test Instead of a Full Hour
In theory, the purest way to measure FTP is to ride as hard as possible for a full 60 minutes and record the average power. In practice, almost nobody paces a true hour-long maximal effort well, and the mental toll of doing so regularly for retesting purposes is brutal. Hunter Allen and Andrew Coggan, who popularized power-based training for cyclists, found that a well-paced 20-minute maximal effort correlates closely with what a rider can sustain for an hour — specifically, most trained cyclists can hold about 95% of their 20-minute power output for a full 60 minutes. That's where the formula in this calculator comes from: FTP = 20-minute average power × 0.95. It's a practical, well-validated shortcut, not a perfect substitute for lab threshold testing, but it's accurate enough to build real training zones around.
The 7 Coggan Power Zones and What They're For
Once you know your FTP, everything else is expressed as a percentage of it, which is what makes power-based training so useful — your zones scale precisely to your own fitness rather than a generic chart. Zone 1 (Active Recovery, below 55% of FTP) is easy spinning meant to promote blood flow without adding training stress. Zone 2 (Endurance, 56–75%) is your aerobic base-building zone, where you can hold conversation and ride for hours. Zone 3 (Tempo, 76–90%) is a brisk, purposeful effort that builds muscular endurance without the recovery cost of harder work. Zone 4 (Threshold, 91–105%) sits right around your FTP itself and is where classic "sweet spot" and threshold intervals live. Zone 5 (VO2max, 106–120%) targets your aerobic ceiling with hard 3–8 minute efforts. Zone 6 (Anaerobic Capacity, 121–150%) covers short, explosive efforts like attacks and hard climbs. Zone 7 (Neuromuscular Power, above 150%) covers maximal sprints lasting only a few seconds, where aerobic metabolism barely factors in at all.
Putting Your FTP to Work
Once you have a number, use it to structure your training rather than just admiring it. A coached plan will typically assign specific workouts to specific zones — sweet spot intervals at 88–94% of FTP for building threshold, VO2max intervals at 110–120% for raising your aerobic ceiling, and long endurance rides in Zone 2 for base fitness. Pacing races and group rides also gets easier: if you know a climb will take 12 minutes, you know roughly what percentage of FTP you can sustain for that duration without cracking. Many riders also track FTP relative to body weight (watts per kilogram), since that ratio determines climbing performance far more than raw wattage does.
Caveats Worth Knowing
A 20-minute field test is only as good as the pacing and effort behind it — going out too hard in the first five minutes and fading will understate your true FTP, while an overly conservative effort will do the same in the other direction. Environmental factors like heat, wind (if outdoors), and fatigue from previous training days can all shift the number on a given day. Because fitness changes over time, treat any FTP estimate as a snapshot rather than a fixed constant: retest every 6–8 weeks during a structured training block so your zones stay aligned with your current form, and adjust your training plan whenever a retest shows a meaningful shift.
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