Understanding The Energy You Burn
Exercise energy is often reported in Calories by watches and in kilojoules by bike computers and gym machines. These guides explain what the numbers mean, how they are estimated, and how to compare them with the kilojoules in food.
Most estimates use MET values, multiples of the energy you use at rest, combined with your body weight and the time you spend active. They are good averages, but your personal burn can be 10-20% higher or lower.
Calculate Your Own Numbers
- Exercise kJ calculator, 25 activities, any body weight.
- Daily kJ calculator, see how activity changes your daily needs.
- kJ to calories chart, walking and running time for every value.
Remember that exercise is excellent for health but a slow way to cancel out food energy, which is why eating patterns and activity work best together.
Gross Vs Net Energy
Most calculators and devices report gross energy, everything you burn during the activity, including the energy your body would have used anyway. Net energy subtracts that resting baseline (about 1 MET). For a 30-minute walk at 5 km/h, a 70 kg adult burns about 538 kJ gross but only around 384 kJ more than sitting still. Knowing which figure you are looking at avoids overestimating how much extra food an activity allows.
Energy use per kilometre also changes with terrain, load and pace: hills, sand, trails and backpacks all raise it, while efficient cycling on flat roads lowers it. Treat every figure as a helpful estimate rather than an exact measurement.