Heart Rate to Watts Calculator

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Estimate your cycling power output based on current heart rate and known performance data.

Target/Current Heart Rate (BPM)

Resting Heart Rate (BPM)

Reference Heart Rate (e.g. HR at FTP)

Reference Power (Watts at Reference HR)

Estimated Power

0 Watts

Understanding the Connection Between Heart Rate and Watts

In endurance sports like cycling, "Watts" represent the actual work being performed (external load), while "Heart Rate" represents the body's physiological response to that work (internal load). While a power meter provides an objective measure of intensity, your heart rate provides context on how hard your cardiovascular system is working.

Converting Heart Rate to Watts isn't an exact science because heart rate is affected by temperature, caffeine, fatigue, and hydration. However, by using a Reference Point—such as your Heart Rate at Functional Threshold Power (FTP)—you can create a linear estimation of your power output for a given heart rate.

Realistic Example:
If your "Reference" state is 250 Watts at 170 BPM, and your resting heart rate is 60 BPM, and you are currently riding at 140 BPM, this calculator helps you estimate what your current wattage would be in stable conditions.

The Science of Efficiency Factor (EF)

This calculator utilizes a modified Karvonen formula. Instead of just looking at the raw BPM, it accounts for your heart rate reserve (the range between resting and maximum effort). This provides a more accurate representation of how power scales across your aerobic zones.

Why Estimate Watts from Heart Rate?

Power Meter Failure: If your power meter battery dies mid-ride, you can use heart rate to stay within your training zones.
Indoor Training: Many riders have smart trainers indoors but no power meter on their outdoor bikes.
Monitoring Fatigue: If your heart rate is significantly higher than usual for a specific wattage (decoupling), it may indicate overtraining or dehydration.

Key Limitations

It is important to remember that Aerobic Decoupling occurs during long rides. As you fatigue, your heart rate may rise even if the wattage remains constant (cardiac drift). Therefore, this calculator is most accurate during the first 60-90 minutes of exercise or in a well-cooled environment.