Your FTP is 95 percent of the average power held over an all-out 20-minute test. From that single number come the seven training zones, and your power to weight if you enter your weight.
The calculator does the arithmetic. The rest of this page explains where the 95 comes from, what FTP doesn't tell you, and why it sometimes moves ten watts from one week to the next without anything having changed in your legs.
Estimated FTP—
Your power zones
| Zone | % FTP | Watts |
|---|
What FTP is, and what it isn't
FTP is the power you can hold for roughly an hour, all out. Nothing more.
It isn't a physiological threshold. Lactate threshold gets measured in a lab with blood samples, and it doesn't land in exactly the same place for everyone. FTP is a field approximation, built to be measurable with a power meter and a stopwatch. It's useful because it's repeatable, not because it's exact.
Its real function is being a unit of measure. A session described as four times eight minutes at 105 percent of FTP means the same thing to everybody, whereas in absolute watts it would mean nothing. That's what FTP delivers: a shared language for prescribing intensity.
Why 95 percent of the 20-minute test
Because a full hour flat out is hard to execute properly, and because nobody willingly repeats it every six weeks.
Twenty minutes fits inside a normal session and is mentally manageable. The 0.95 factor comes from the observation that average power over twenty minutes runs about five percent above what you'd hold for an hour. It's an average, and it carries the same limit as every average: someone very endurance-oriented will hold closer to 97 percent of their twenty-minute power for an hour, someone very explosive closer to 92.
Other protocols exist, from the ramp test to the eight-minute test. They return slightly different numbers, which doesn't matter at all as long as you keep the same one over time. Changing protocol between two measurements makes the comparison unusable.
The protocol, in full
Twenty minutes of progressive warm-up, building gently to a moderate intensity.
Five minutes flat out, as an opener. This is the step everyone skips, and it changes the result: without it, the first three minutes of the test go into reaching working level instead of producing power.
Ten very easy minutes to recover.
Then twenty minutes flat out, on a steady stretch of road or on a trainer. Pacing matters as much as fitness: the first five minutes should come out slightly below what you think you can hold, and the average power of the last five should equal or beat the first five. A test started too hard returns a number that's too low and an unpleasant experience.
Ten minutes to cool down. The test costs a hard session: it goes on a day when you're fresh, not at the end of a loading block.
The seven zones, and what each is for
Zone 1 is for recovering and pedalling without paying for it. Zone 2 is the volume zone, where the aerobic base gets built: long rides live there, and it's the most productive zone per hour invested over the long term.
Zone 3, tempo, is comfortable and moderately useful. Zone 4, around FTP, is the one that moves the number itself, in intervals of eight to twenty minutes.
Zone 5 works the aerobic ceiling in repetitions of three to five minutes. Zone 6 works anaerobic capacity over thirty seconds to three minutes. Zone 7, above 150 percent, only holds for a few seconds and serves sprinting and neuromuscular power.
One remark worth more than the list: most amateur cyclists spend too much time in zone 3 and not enough in zones 2 and 4. Tempo feels like working hard while producing little adaptation, and it eats the freshness the sessions that do build fitness require.
Watts per kilo, and when it matters
Power to weight decides climbing, and almost nothing on the flat.
Uphill, gravity dominates: the ratio of watts to kilos determines speed. On the flat, air resistance dominates, and absolute watts are what count, with aerodynamic position right behind. A heavy, powerful rider is fast on the flat and slow in the mountains, a light rider the reverse, and both can have the same FTP.
| Profile | Watts per kilo |
|---|---|
| Occasional rider | 2.0 to 2.5 |
| Regular practice | 2.5 to 3.2 |
| Solid club level | 3.2 to 4.0 |
| Strong amateur | 4.0 to 5.0 |
These bands describe an adult man and shift with sex and build. They're for placing yourself, not judging yourself, and they say nothing about the ability to hold a five-hour ride, which is a different quality.
What moves the number without you improving
Four causes, and they explain most of the surprises.
Heat first. A test in a poorly ventilated room comes out five to ten watts below the same test outdoors in cool weather. The fan isn't a comfort, it's a measurement variable.
The meter next. Two different power meters can read two to three percent apart, which is enough to invent a gain or a loss. Comparing FTPs measured on two different devices means nothing.
Freshness. A test at the end of a loading block reads low, a test after an easy week reads high. The number reflects the state of the day as much as the state of your fitness.
And pacing. A twenty minutes started ten watts too high pays for it with a collapse at halfway, and the final average suffers more than the opening error would suggest.
FAQ
Is FTP really your one-hour power?
Roughly, and the approximation is openly declared. Some people hold their FTP for forty-five minutes, others for seventy. The value of the measurement comes from its repeatability, not from matching a duration exactly.
Do I really need the five minutes flat out before the test?
Yes, and it's the step most often skipped. Without it, the opening minutes of the twenty go into reaching working level rather than producing power, and the result comes out mechanically lower.
How often should I retest?
Every six to eight weeks, under the same conditions and with the same protocol. More often only measures the fatigue of the moment. And plenty of structured plans nudge FTP up when zone 4 sessions start feeling easy, without running a test at all.
Can I estimate FTP without a power meter?
Not usefully. FTP is a measurement in watts, and speed doesn't substitute for it because speed depends on wind, gradient and position. Without a meter, heart rate and feel remain valid reference points, and they don't produce an FTP.
Should indoor and outdoor FTP match?
No, and the gap almost always runs the same way: indoors reads lower, by five to ten watts, because of heat and the absence of cooling. Keeping two values, one per context, is more honest than forcing a single one.
What about the ramp test?
It's shorter and less unpleasant, and it overstates FTP for explosive riders, sometimes by ten watts. It suits regular tracking well, as long as you don't compare its result against a twenty-minute test.
Should I lose weight to improve watts per kilo?
The ratio has two terms, and working on the numerator is safer. Losing weight without watching power often brings both down, and climbing gains nothing. The reliable route is raising FTP at stable weight.
Is FTP useful if I ride for fun?
It's useful for knowing what intensity to ride at, which helps even without a goal. Without a reference point, most rides end up in zone 3, the zone where you tire the most to progress the least.
Can I enter my weight in pounds?
Yes, the kg or lb switch takes either, and the output stays in watts per kilo. That isn't an oversight: W/kg is the worldwide cycling standard, watts per pound exists nowhere, and showing both would invent a unit nobody could compare against.
A number doesn't build a season
FTP tells you what intensity to pedal at. It doesn't tell you how many rides, how to spread them, or when to back off, and that's where seasons come apart. The Vitality Archetype test measures your profile across 5 dimensions in 27 questions and 3 minutes, then generates a week calibrated for your recovery and your available time, adjusted with the feedback from each session. The zones then become sessions, placed on the right days.