An FTP (Functional Threshold Power) Calculator is a sports science tool that estimates a cyclist's Functional Threshold Power, which is a key measure of their aerobic fitness. FTP is defined as the highest average power, measured in watts, that a cyclist can sustain for approximately one hour. Directly performing a one-hour, all-out test is incredibly demanding, so shorter, more practical test protocols have been developed. This calculator takes the average power data from one of these shorter tests (such as a 20-minute or 8-minute test) and applies a specific correction factor to estimate the one-hour FTP value. This calculated FTP is the single most important number in power-based training, as it is used to set personalized training zones and track fitness improvements over time.
formula of FTP (Functional Threshold Power) Calculator
The formula used to calculate FTP depends on the specific test protocol you follow. Below are the most common methods.
1. FTP from a 20-Minute Test
This is the most common and widely accepted method for estimating FTP.
Formula:
FTP = Average Power from 20-Minute Test * 0.95
- Average Power from 20-Minute Test: The average power in watts sustained over the 20-minute, all-out effort.
- 0.95: The standard correction factor. It takes 95% of the 20-minute power to estimate the power you could hold for a full hour.
2. FTP from an 8-Minute Test
This protocol uses two 8-minute, all-out efforts.
Formula:
FTP = Highest Average Power from either 8-Minute Test * 0.90
- Highest Average Power from either 8-Minute Test: Use the higher of the two average power values from your two 8-minute efforts.
- 0.90: The standard correction factor for this protocol, taking 90% of the value.
3. FTP from a Ramp Test
A ramp test involves a progressive increase in power until failure.
Formula:
FTP = Best 1-Minute Average Power from Ramp Test * 0.75
- Best 1-Minute Average Power from Ramp Test: The average power from the final, successfully completed minute of the test.
- 0.75: The standard correction factor for most ramp test protocols, taking 75% of the best 1-minute power.
Power-to-Weight Ratio (W/kg) Based on FTP
Once you know your FTP, you can calculate your power-to-weight ratio, which is a key indicator of climbing performance. This table shows the classification of different power-to-weight ratios for cyclists.
| Power-to-Weight Ratio (W/kg) | Rider Category |
| < 2.0 W/kg | Untrained / Novice |
| 2.0 - 3.0 W/kg | Recreational / Enthusiast |
| 3.0 - 4.0 W/kg | Experienced / Cat 4-5 Racer |
| 4.0 - 5.0 W/kg | Strong Amateur / Cat 1-3 Racer |
| > 5.0 W/kg | Elite / Professional |
Example of FTP (Functional Threshold Power) Calculator
A cyclist has just completed a 20-minute FTP test using their power meter.
First, they analyze the data from their cycling computer.
- Test Duration: 20 minutes
- Average Power: 300 watts
Next, they apply the standard formula for a 20-minute test.
FTP = Average Power from 20-Minute Test * 0.95
FTP = 300 * 0.95
FTP = 285 watts
Therefore, the cyclist's estimated Functional Threshold Power is 285 watts. They can now use this number to set their training zones.
Most Common FAQs
To measure your FTP, you need a way to measure your power output in watts. This requires a bicycle equipped with a power meter or an indoor smart trainer that has a built-in power meter. You will also need a cycling computer or a training app (like Zwift, TrainerRoad, or Wahoo SYSTM) to record the power data during your test.
It is generally recommended to test your FTP every 4 to 6 weeks during a structured training block. This allows you to track your fitness progress and ensure that your training zones remain accurate and effective. You should also consider re-testing after a significant break from training or if you feel your fitness has changed substantially.
FTP is the cornerstone of power-based training because it provides an accurate, objective measure of your current fitness level. All of your training zones—from active recovery to anaerobic capacity—are calculated as percentages of your FTP. By training in these specific zones, you can target different physiological systems in your body to achieve specific training adaptations, making your training much more efficient and effective.