The quick estimate: MET
MET stands for metabolic equivalent. 1 MET is roughly your energy use at rest, about 1 kcal per kilogram of body weight per hour. The Compendium of Physical Activities, a scientific collection of measured values, assigns a MET value to each activity. The calculation is simple:
kcal = MET × body weight in kg × duration in hours
MET values for road cycling from the 2024 Compendium:
- leisure, under 10 mph (16 km/h): 4.0 MET
- 10 to 11.9 mph (16 to 19 km/h): 6.8 MET
- 12 to 13.9 mph (19 to 22 km/h): 8.0 MET
- 14 to 15.9 mph (22.5 to 25.5 km/h): 10.0 MET
- 16 to 19 mph (26 to 30.5 km/h) without drafting: 12.0 MET
- over 20 mph (32 km/h), racing without drafting: 16.8 MET
Example: You weigh 70 kg and ride for 2 hours at about 12.5 mph (20 km/h). That gives 8.0 × 70 × 2 = 1120 kcal.
This includes your resting burn (1 MET). If you only want to know what the ride cost on top, use the MET value minus 1: 7.0 × 70 × 2 = 980 kcal.
MET values are averages. Headwind, climbs, drafting in a group and your bike change the effort a lot. Treat the result as a rough estimate.
Most accurate: with a power meter
A power meter measures the work you put into the pedals. That gives a much better estimate of your burn than speed or heart rate.
- Work in kilojoules = average power in watts × duration in seconds ÷ 1000
- Your body turns only about a fifth of the energy into propulsion, the rest becomes heat. In a lab study, this efficiency averaged 19.8 percent in trained cyclists.
- So for every kilojoule of work you use about 5 kilojoules of energy. Since 1 kcal equals 4.184 kJ, that is about 1.2 kcal per kilojoule of work.
Example: 180 watts for 2 hours gives 180 × 7200 ÷ 1000 = 1296 kJ of work. That is about 1296 × 1.2 ≈ 1550 kcal.
Efficiency varies between people and rises slightly with power. If you ride more efficiently, your burn is a little lower. This is still an estimate, but one with a solid basis.
With heart rate
Without a power meter, watches and apps usually estimate your burn from heart rate. A well-known equation comes from Keytel and colleagues (2005). It uses heart rate, body weight, age, sex and, if known, maximal oxygen uptake (VO2max). With VO2max the model explained about 83 percent of the differences in energy expenditure in the study, without it about 73 percent.
For a group, that is fairly good. For you alone, the number can still be far off, especially if the wrist heart rate is inaccurate. More on that in How accurate are smartwatch calories?
Which method fits you?
- You have a power meter: use the power method. It is the most accurate of the three.
- You only know speed and duration: use MET values as a rough estimate.
- You only have a watch with heart rate: treat its number as an estimate, not an exact value.
How it works in HabitHelm
HabitHelm takes your rides from Strava automatically, including Garmin rides via the Strava connection. The recorded burn goes into your daily target with care, and on hard days your carbohydrate target goes up. How it is calculated is explained under Training day calories, the setup under Connect Strava.
Sources
- Herrmann SD, Willis EA, Ainsworth BE et al. (2024): 2024 Adult Compendium of Physical Activities: A third update of the energy costs of human activities. Journal of Sport and Health Science 13(1):6–12. doi.org/10.1016/j.jshs.2023.10.010, cycling MET values: pacompendium.com/bicycling
- Moseley L, Jeukendrup AE (2001): The reliability of cycling efficiency. Medicine & Science in Sports & Exercise 33(4):621–627. doi.org/10.1097/00005768-200104000-00017
- Keytel LR, Goedecke JH, Noakes TD et al. (2005): Prediction of energy expenditure from heart rate monitoring during submaximal exercise. Journal of Sports Sciences 23(3):289–297. doi.org/10.1080/02640410470001730089