Free tool · Training
Cycling calories calculator from power
Short answer
A power meter measures the work you do: watts × seconds. Your body is only about 19.8% efficient, so it burns about five times that much energy. 200 W for 60 minutes is 720 kJ of work and roughly 869 kcal burned, about 1.2 kcal for every kJ on your bike computer.
Last reviewed 28 October 20263 published sourcesNot medical advice
Reps keeps track of this for you on iPhone, iPad and Apple Watch.
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Use the average power from a power meter or smart trainer and the ride time.
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| Average power | Work per hour | Calories per hour |
|---|---|---|
| 100 W | 360 kJ | 435 kcal |
| 150 W | 540 kJ | 652 kcal |
| 200 W | 720 kJ | 869 kcal |
| 250 W | 900 kJ | 1,086 kcal |
| 300 W | 1,080 kJ | 1,304 kcal |
Gross efficiency
Gross efficiency is work accomplished divided by energy expended (Artetxe-Gezuraga et al., 2019). In Moseley and Jeukendrup's reliability study it averaged 19.8% (Moseley & Jeukendrup, 2001), and young elite cyclists averaged 19.3–19.4% across a season (Artetxe-Gezuraga et al., 2019).
Efficiency depends strongly on work rate, mainly because the energy you burn even at zero power matters less as power rises (Ettema & Lorås, 2009). Moseley and Jeukendrup found it lower at 95 and 130 W than at 165 W and above (Moseley & Jeukendrup, 2001), so easy rides burn a little more than this calculator shows. If you know your own efficiency from a lab test, enter it.
Related tools
Without a power meter, the heart rate calories calculator works from heart rate. To set training power, start with the FTP calculator.
Every ride, counted toward your load
Reps tracks how hard each workout was from your Apple Watch heart rate and shows whether your load is building, holding or easing off.
Free to download · iPhone, iPad and Apple Watch
Common questions
How do I convert watts to calories?
Work (kJ) = average watts × seconds ÷ 1,000. Energy burned (kcal) = work ÷ gross efficiency ÷ 4.184. At about 20% efficiency, each kJ of work costs about 1.2 kcal.
What is gross efficiency in cycling?
The share of the energy you burn that ends up as work on the pedals: work done ÷ energy expended. Cyclists in published studies average around 19–20%, and the rest is lost as heat.
Why does my bike computer show kJ and not calories?
kJ is the work measured by the power meter, which is exact. Calories burned depend on your efficiency, which the computer has to assume. At a typical 19–20% efficiency, calories burned come out about 20% higher than the kJ figure.
Sources
Figures on this page were checked against these publications on 28 October 2026.
- Moseley L, Jeukendrup AE. The reliability of cycling efficiency. Medicine & Science in Sports & Exercise. 2001;33(4):621–627. doi.org/10.1097/00005768-200104000-00017
- Artetxe-Gezuraga X, Maldonado-Martín S, Freemye BG, Cámara J. Gross efficiency and the relationship with maximum oxygen uptake in young elite cyclists during the competitive season. Journal of Human Kinetics. 2019;67:123–131. doi.org/10.2478/hukin-2018-0089
- Ettema G, Lorås HW. Efficiency in cycling: a review. European Journal of Applied Physiology. 2009;106(1):1–14. doi.org/10.1007/s00421-009-1008-7
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