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Cycling Calorie Burn by Power Calculator

Turn your average power into calories, grams of carbs and fat, and an on-bike fuelling target.

How it is calculated

Mechanical work is kJ = W × minutes × 60 ÷ 1000. Because 1 kJ equals 0.239006 kcal, work in kcal is multiplied by 0.239006 and divided by gross efficiency, kcal = kJ × 0.239006 ÷ (eff ÷ 100). Efficiency defaults to 23 % when left empty or out of range. Intensity is W ÷ FTP. The carbohydrate share is 0.25 + 0.90 × (intensity − 0.35), clamped between 15 % and 95 %; carbs are kcal × share ÷ 4 and fat is kcal × (1 − share) ÷ 9, both in grams. The fuelling target is 30 g/h below 56 % of FTP, 60 g/h below 76 % and 90 g/h above. Power, duration and FTP are all required.

Worked example

A rider averages 200 W for 120 minutes with an FTP of 260 W. Work is 200 × 7,200 s ÷ 1000 = 1,440 kJ, which is about 344 kcal of mechanical work. At 23 % efficiency that becomes 1,496 kcal, or 748 kcal/h. Intensity is 200 ÷ 260 = 76.92%, so the carbohydrate share is about 63 %, giving 235 g of carbs and 62 g of fat. Above 76 % of FTP the target is 90 g/h.

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Common mistakes

  • Leaving FTP empty: the tool needs it to set intensity and returns no result without it. Use a recent test value, not a goal figure.
  • Entering the duration in hours. The field is in minutes, so 2 hours is 120.
  • Using normalised or peak power: the model assumes a steady ride at the average watts you enter, so a stop-start ride will be off if you feed it average power with long coasting included or excluded inconsistently.
  • Reading the kJ figure as calories. Kilojoules of work are close to kcal burned only because efficiency is near 24 %; the tool already makes that conversion, so do not add it again.
  • Expecting efficiency to be personal: the 23 % default is a fixed assumption, so change the field if you know a different gross efficiency, since kcal scales directly with it.

Sources

About this calculator

A power meter measures mechanical work output directly in watts, which converts to calories far more accurately than heart rate or speed because it isn’t affected by drafting, wind, terrain or cardiac drift over a long ride. The conversion uses your average power multiplied by ride duration to get kilojoules of mechanical work, then divides by gross efficiency (typically around 20-25% for trained cyclists) to estimate the metabolic calories actually burned, since the body wastes most of the energy it converts as heat.

Cyclists training with a power meter use this calculation to set nutrition targets for long rides — knowing calories burned, split into the carbohydrate and fat contribution at a given intensity, tells you how many carbs per hour you need to eat to avoid bonking, since higher-intensity efforts shift fuel use toward carbohydrate and away from fat. It’s more reliable for fueling decisions than calorie estimates from a bike computer’s default formulas, which are usually just rough speed- or heart-rate-based guesses.

Average power and ride time set the work done; FTP sets how hard the ride was, and an optional gross efficiency fine-tunes the conversion, giving total calories, the carbohydrate/fat split and a carbs-per-hour fuelling target.

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