How to estimate your FTP: ramp test vs 20-minute test

Almost every structured plan is built on one number: your FTP. So it is worth knowing how to estimate it honestly — and what to do when two perfectly good tests hand you two different answers.

What FTP actually is

FTP — functional threshold power — is the highest average power, in watts, that you can sustain for roughly an hour. It sits near the line between efforts you can hold for a long time and efforts that force you to stop within minutes. That is why it is so useful: once you know it, every training intensity can be written as a percentage of it, and your power zones fall out automatically.

The catch is that almost nobody wants to ride all-out for a full hour to measure it directly. So in practice we estimate FTP from a shorter effort. The quickest way to get a number is to plug a test result into the FTP calculator, but it is worth understanding what the tests are doing first.

The two field tests worth using

There are many protocols, but two cover almost everyone. They trade off precision against how easy they are to execute well.

The 20-minute test (× 0.95)

Warm up thoroughly, then ride a maximal, evenly paced 20-minute effort. Take the average power and multiply by 0.95:

The 5% reduction exists because you can hold more power for 20 minutes than for a full hour. Its strength is that it is a genuinely long, threshold-like effort, so it maps closely to what FTP is meant to represent. Its weakness is pacing: go out too hard and you fade and under-record; start too cautiously and you leave watts on the table. It also takes a good day and a fair amount of mental grit. A short five-minute hard effort before the test, then easy spinning, helps clear the freshness that would otherwise inflate your first few minutes.

The ramp test

Start easy and ride steadily rising power — commonly increasing every minute — until you cannot hold the next step. Your FTP is estimated from the final minutes, usually about 75% of your best one-minute power. The whole thing takes around 20–25 minutes including warm-up.

Its strengths are convenience and repeatability. There is no pacing skill involved — you simply ride until you stop — so it is hard to get "wrong," and it is easy to reproduce the same way every few weeks. That makes it excellent for tracking change. Its weakness is that the final minutes borrow heavily from your anaerobic system, which is not the system FTP is about. Riders built for short, sharp efforts often get a ramp number that overstates their true one-hour power.

Why the two tests give different numbers

The gap between the two is not measurement error — it is a real difference in what they are asking your body to do. A ramp test finishes with a short, brutal, largely anaerobic push. A 20-minute test is a long aerobic grind. Riders are not all built the same across those two demands:

• Punchy, sprint-leaning riders tend to score higher on the ramp test, because their big anaerobic contribution lifts that final minute — and the estimate with it.
• Steady, aerobic "diesel" riders often do better on the 20-minute test, where their ability to hold a hard effort for a long time is exactly what is being measured.

This is why copying a friend's protocol and comparing numbers is a trap. A 250-watt ramp FTP and a 250-watt 20-minute FTP can describe two very different engines. What matters is comparing a test against your own earlier results using the same method.

Which number to actually train with

Here is the part most guides skip. FTP is an estimate, not a lab value, and the point of having it is to make your workouts land at the right intensity. So the number you should train with is the one that does that — which is usually, but not always, exactly what your test produced.

• Pick one protocol and stick with it. The trend across repeated tests tells you more than any single result. Switching methods every time makes your history meaningless.
• Set your zones, then sanity-check by feel. A classic check is a threshold session like 2×20 minutes at 95–100% of FTP. It should be hard but completable. If it feels comfortable, your FTP is probably set too low; if you cannot finish it, it is set too high.
• Use a working FTP, not a trophy FTP. If the ramp flattered you, it is fine to train a few percent below the test number so your intervals are honest. Many riders train to a figure that sits slightly off their best test — that is normal, not cheating.
• Do not retest constantly. Every 4–8 weeks of consistent training, or after a clear block of work, is plenty. Testing too often adds fatigue without new information.

In other words: let the test give you a starting number, then let your actual sessions be the final judge. If you are chasing a bigger figure for its own sake, it is worth remembering that consistency and fatigue management usually matter more than FTP gains for real-world improvement.

What your FTP number actually means

Once you have a number you trust, it becomes the anchor for everything else. Your training zones are defined as bands around it — roughly, endurance at 56–75%, sweet spot around 88–94%, threshold near 95–105%, and VO2 max work at 106–120%. Get the FTP roughly right and every one of those targets is roughly right too; get it badly wrong and every session inherits the error. That is the real reason the number matters — not the bragging value, but the fact that your whole week is scaled to it, including how much easy Zone 2 riding you do.

Raw FTP in watts is only half the picture, though. A given FTP means something very different for a light climber than for a heavy rider, so for comparing engines the fairer figure is power-to-weight — divide your FTP by your body weight with the W/kg calculator. If you want to know whether your number is strong for your level, the what is a good FTP guide and the FTP benchmarks page put it in context.

How SmarterTraining thinks about this

SmarterTraining treats FTP as a working estimate, not a verdict. It uses your FTP to scale each session, but it also watches how your recent rides actually go and adjusts around your fatigue, recent training, and the time you have — so a slightly stale or slightly optimistic number does not quietly derail a week of training.

The goal is not a perfect one-off measurement. It is workouts that stay the right difficulty as your fitness moves, without you having to re-test and re-plan every time life gets in the way.

Takeaway

Takeaway: Estimate your FTP with either a ramp test (about 75% of best one-minute power) or a 20-minute test (average × 0.95), and do not be surprised when they differ — they lean on different systems. Pick one method, track it over time, and train with the number that makes your threshold sessions genuinely hard but finishable. The best FTP is not the biggest one; it is the one your training is honestly built on.