Inputs
Results
Enter power and duration to compute results.
Formula
Mechanical work (J) = Power (W) × Time (s)
Metabolic energy (kJ) = Mechanical work (kJ) / Efficiency
Calories (kcal) = Metabolic energy (kJ) / 4.184
Efficiency is dimensionless (e.g., 0.22 = 22%).
Why efficiency matters
Cycling output power measures mechanical work at the pedals. Your body expends more energy than the work measured at the drivetrain because muscles are not perfectly efficient. Selecting gross or net options changes the assumed ratio between mechanical output and total metabolic energy. You may also choose a custom value to match lab testing.
FAQs
Accuracy depends on the quality of the power data and the efficiency chosen. Lab measured efficiency provides the best fit while typical values give useful estimates for training.
Gross reflects total energy cost including resting processes. Net is closer to the extra energy above rest during exercise. Many field estimates use gross 18–24% while some sports science reporting uses net 22–25%.
Resting energy is approximated with 1 MET which expends about 1 kilocalorie per kilogram each hour. Body mass scales this baseline to your size so net exercise calories can be estimated realistically.
The formula only uses average power and time so cadence and terrain affect results only through their influence on power output. The more accurate your power data the better the estimate.
Yes. If you have a measured efficiency from an exercise test use Custom mode and enter that fraction. You can also tune the value to align with known fuelling during steady rides.