Cycling Calories From Power Calculator
Convert average power and ride time into calories burned and mechanical work in kilojoules — the power-meter way to measure a ride.
How it works
work (kJ) = power (W) × time (s) ÷ 1000 · calories = work ÷ 4.184 ÷ gross efficiency
A power meter measures the mechanical work you deliver to the pedals in joules; a watt held for a second is a joule. Because the human body converts food energy to pedal work at only about 20–25% efficiency, the calories you actually burn are roughly four times the mechanical work — but that work is measured in kJ and food energy in kcal (1 kcal = 4.184 kJ), and the two conversions nearly cancel. That is the well-known coincidence that kilojoules on your head unit ≈ kilocalories burned.
Worked example
200 W for 1 h 30 min (5,400 s): work = 200 × 5,400 ÷ 1000 = 1,080 kJ. Calories = 1,080 ÷ 4.184 ÷ 0.24 ≈ 1,076 kcal — almost identical to the kilojoule figure.
Frequently asked questions
Why are power-based calories more reliable than heart-rate estimates?
Power measures the actual work you do, independent of caffeine, heat, fatigue or fitness. Heart-rate calorie estimates infer effort indirectly and drift with all of those factors, so two identical rides can report very different numbers.
What efficiency should I use?
Gross cycling efficiency is typically 20–25%, and 24% is a common default that makes kJ ≈ kcal. Well-trained cyclists sit slightly higher; if you have lab data use your measured value, otherwise the default is fine.
Does this include calories from just being alive?
No — it is the energy cost of the ride above rest, based on work done. Your basal metabolism over the same time is separate and much smaller per minute than hard riding.
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This calculator is for educational purposes. Double-check important results before acting on them.