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Estimate cycling power in watts from speed, rider weight, road gradient, wind, and aerodynamic drag on climbs and flats.
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Power meters measure mechanical work in kilojoules. Human gross mechanical efficiency on a bike is approximately 20-25%. Total metabolic energy is therefore kJ of work divided by efficiency factor.
Calories = (Avg Power × Duration_seconds) / 1000 / Efficiency; where Efficiency ≈ 0.20–0.25At typical cycling efficiency (20-25%), total kJ of work approximately equals total kcal burned. This is because the 4.184 kJ/kcal conversion and the ~23% efficiency roughly cancel out, making kJ ≈ kcal a practical field shortcut.
kcal ≈ kJ (within ~5% for trained cyclists)Updated: July 2026
Trained cyclist doing a Zone 2 base ride averaging 180 watts for 2 hours.
→ ~1,296 kJ ≈ 1,296 kcal burned
High-intensity training session with intervals, averaging 250W normalized over 60 minutes.
→ ~900 kJ ≈ 900 kcal burned
Speed is heavily influenced by wind, gradient, drafting, and road surface. A 30 km/h ride into a headwind burns far more than 30 km/h with a tailwind. Power is the only reliable metric.
Normalized Power (NP) reflects physiological cost of variable efforts but should not be used directly for calorie calculation. Use average power (work done / time) for energy expenditure.
Power meter calories include your basal metabolic rate during the ride. For net exercise calories above rest, subtract approximately 1 kcal/kg/hr of body weight.
Calculate cycling energy expenditure from average power output and ride duration. Power-based calorie estimation is the gold standard in cycling, far more accurate than speed or heart rate methods because it directly measures mechanical work output.