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Watts to Calories Cycling Calculator

Enter average watts and ride time to estimate calories burned.

How it is calculated

Mechanical work is W(kJ) = watts × minutes × 60 ÷ 1000. It is turned into kilocalories with W(kcal) = W(kJ) × 0.239006. Because muscles waste most of the fuel as heat, the energy your body actually spends is calories = W(kcal) ÷ (efficiency ÷ 100). The optional efficiency field is gross efficiency in percent; if you leave it empty, enter 0 or a negative number, the tool uses 24. Negative watts or minutes return no result. The tool outputs the total burned kcal, the work in kJ, the work in kcal and the efficiency used, rounded for display.

Worked example

Take an average of 200 W for 60 minutes. Seconds = 60 × 60 = 3,600, so work = 200 × 3,600 ÷ 1000 = 720.0 kJ. In kcal that is 720 × 0.239006 ≈ 172 kcal. With the default 24% efficiency, 172 ÷ 0.24 gives 717 kcal burned. Setting efficiency to 20 instead raises the figure to 860 kcal.

Try this example →

Common mistakes

  • Entering the duration in hours instead of minutes; one hour must be typed as 60, not 1.
  • Using peak or sprint watts instead of the ride's average power, which inflates the total. Average power should include any coasting at zero watts if the minutes include it.
  • Reading the "work" lines as calories burned. Work in kcal is only the mechanical output; the burned figure is larger because of efficiency.
  • Typing efficiency as a fraction such as 0.24; it is a percentage, so 0.24 would mean 0.24% and give an absurd result.
  • Treating the result as exact: the default 24% is an assumption, and a few points of difference in true efficiency shift the total by hundreds of kcal on long rides.

About this calculator

A power meter measures mechanical output in watts, and multiplying watts by time gives energy in joules (1 W = 1 J/s), which converts to kilocalories at 1 kcal = 4184 J. But the body isn't 100% efficient at turning food energy into pedaling power — gross metabolic efficiency for cycling is typically around 20-25%, meaning the calories actually burned are roughly 4-5 times the mechanical work done, not equal to it.

This calculator takes your average power output and ride duration, converts the mechanical work to joules, and applies a standard cycling efficiency factor to estimate calories burned. Cyclists training with a power meter use it to cross-check the calorie estimates from their head unit or Strava, and cycling coaches use it to set nutrition targets around planned training loads measured in watts rather than heart rate.

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Comments (1)

  • Editorial team

    A handy rule of thumb falls out of the maths: at the default 24 percent efficiency, kilocalories burned come out almost equal to the kilojoules of work. In the example, 720 kJ of work gives 717 kcal. Many power meters and head units show kJ, so you can compare that number with the burned figure directly. If you have a different efficiency estimate, tell us which one you use and how you arrived at it.

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