What Is FTP?
Functional Threshold Power (FTP) is the highest average power, measured in watts, that a cyclist can sustain for roughly one hour. It is the cornerstone metric for setting training zones, pacing time trials, and tracking fitness over time. Because a true one-hour all-out test is brutal, the most common practical method estimates FTP from a shorter 20-minute test.
How to Use This Calculator
After a proper warm-up, ride as hard as you can sustain evenly for 20 minutes and record your average power. Enter that number in watts. Optionally enter your body weight in kilograms to also get your power-to-weight ratio (W/kg), which is useful for comparing climbing performance. The calculator multiplies your 20-minute power by 0.95 to estimate the power you could hold for an hour.
The Formula Explained
The equation is $$\text{FTP} = 0.95 \times P_{20\text{min}}$$ The 5% reduction accounts for the fact that you can produce more power over 20 minutes than over a full hour. Power-to-weight is simply FTP divided by your weight in kilograms: $$\text{W/kg} = \frac{\text{FTP}}{\text{weight}_{kg}}$$
Worked Example
Suppose your 20-minute test averaged 280 watts and you weigh 70 kg. $$\text{FTP} = 0.95 \times 280 = \textbf{266 watts}$$ Power-to-weight = \(266 \div 70 \approx 3.8\ \text{W/kg}\). You would then build training zones around 266 W (e.g. sweet spot at 88–94%, threshold at 95–105%).
FAQ
Is the 20-minute test accurate? It is a widely used estimate. Pacing matters — go out too hard and you'll fade, underestimating FTP.
How often should I retest? Every 4–8 weeks of focused training is typical to track progress.
Can I use a ramp test instead? Yes, but ramp tests use a different multiplier; this calculator is specific to the 20-minute protocol.
