What FTP really is, how to measure it with the 20-minute test without a lab, and why the number drives your training zones and your progress.
## Introduction What exactly is this "FTP" everyone talks about? The honest answer: FTP (Functional Threshold Power) is the power you can hold for roughly one hour at a stretch — your functional threshold in watts. It's the single most important training number in performance-oriented cycling, because all your training zones derive from it.
The practical trick: instead of going all-out for a full hour (almost nobody holds that cleanly), you ride a 20-minute test and take 95 % of your average power as your FTP estimate. The 5 % deduction accounts for 20 minutes being slightly less grinding than a full 60.
Honestly though: FTP correlates well with your real capacity but is not the same as the lab-measured lactate threshold — it's a practical field value, not a physiological law. For training and progress tracking it's worth its weight in gold anyway. This guide walks you cleanly through the test. And don't worry: you need no sports lab and no pricey coach — a power meter or a smart trainer and 30 honest minutes are plenty.
## What You Need - A power meter or a smart trainer — no watt measurement, no real FTP test. - A steady test course — a turbo trainer is ideal, otherwise a long, uninterrupted climb or a flat, traffic-light-free road. - Fresh legs — at least one or two easy days before the test. - A bike computer that shows average power over 20 minutes. - Some experience with even pacing — the test stands or falls on it.
### 1. Warm up properly An FTP test without a warm-up is wasted. Ride 15–20 minutes easy with a few short, hard efforts (say 3× 1 minute brisk) to open up the system. Start cold and you deliver a number that's too low — and then train too easy.
### 2. Ride the 20-minute test evenly Ride 20 minutes as hard as you can just hold steadily. The most common mistake is starting too fast: begin under control, find in the first minutes the maximum pace you can hold to the end. Ideally the last minute even rises slightly, because you had something left.
### 3. Calculate FTP Take your average power over the 20 minutes and multiply it by 0.95. A 300 W average gives 285 W FTP. From now on this number is your anchor for all training zones — memorise it and enter it in your app.
### 4. Derive zones and repeat From FTP come your zones (base, tempo, threshold, VO2max) as percentages. Repeat the test every 4–8 weeks under the same conditions to see progress. Only a reproducible test measures real progress — not day-form. Typical guide values: base below about 75 % of FTP, tempo roughly 76–90 %, threshold 91–105 %, VO2max 106–120 %. Your training app sets the exact limits automatically once the FTP is stored.
## Common Mistakes - Starting too fast. Fix: begin controlled, ride evenly — the last minutes should hurt, not the first. - Testing without a warm-up. Fix: 15–20 minutes of riding in with short efforts. - Testing on tired legs. Fix: one or two easy days before, or you measure fatigue, not power. - Constantly changing test conditions. Fix: always the same course and setup, or the values aren't comparable.
## Safety Notes A 20-minute all-out is a maximal effort — don't take it on with an infection, lingering fever or short on sleep. Warm up properly so heart and muscles are prepared, and stop if you feel dizzy or sick. An FTP value isn't a number worth getting ill for.
Ride the test where a maximal effort is safe: on the turbo trainer or a quiet, open course without junctions and oncoming traffic. In the red your attention to traffic drops rapidly. On the turbo trainer this risk disappears entirely — which is why it is the first choice for maximal tests.
## Pro Tip Eat and fuel before the test as you would before a race and note all the conditions: sleep, course, temperature, tyre pressure, time of day. That makes your next test genuinely comparable — otherwise you never know whether the new number is real progress or just a good day. Comparability is half the science.
### What exactly does FTP mean? FTP stands for Functional Threshold Power — the power you can hold steadily for roughly an hour, in watts. It marks the line between "sustainable for a long time" and "burns out fast". Your training zones derive from it, which is why it's the central control variable in power training.
### How accurate is the 20-minute FTP test? It's a very usable field test: 95 % of your 20-minute average power estimates your hourly power. It correlates strongly with real racing and endurance performance but isn't identical to the lab-measured lactate threshold. For training and progress tracking it's completely sufficient. If you want more precision, you can use a ramp test or a shorter 8-minute test instead — the only thing that matters is that you always use the same method, so the values stay comparable.
### How often should I test my FTP? About every 4–8 weeks, always under conditions as similar as possible (same course, rested, same fuelling). More often achieves little, because real adaptations only show over weeks. What matters is comparability, so you can tell a trend from day-form.
### Do I need a power meter for the FTP test? For a real, comparable FTP value, yes — a power meter or smart trainer measures actual power in watts. You can approximate via heart rate, but it reacts sluggishly and swings with day-form, heat and caffeine. Watts are the hard, instant currency. A smart trainer is the cheapest way in for many: it measures watts reliably and makes the test weather-proof and exactly repeatable.
From City Bike to Road Bike: Your Start