How many calories does cycling burn?
Exactly as many as you put into the pedals, divided by how efficiently your body turns food into pedaling — and that second number is remarkably constant, about 24%. Two hours at 150 W is 1,080 kJ of work and about 1,076 kcal of food. Every activity-table calculator on the internet skips the watts and guesses from speed instead, which is why they can't tell a tailwind from a climb. Here's the same 165 lb rider at four speeds, computed by the physics engine behind our power ↔ speed calculator, with the table's answer beside it:
| Speed | Flat, calm | Into a 15 mph wind | Up a 3% grade | Activity table says |
|---|---|---|---|---|
| 12 mph | 184 kcal/h 51 W | 636 kcal/h | 670 kcal/h | 629 kcal/h 8 METs |
| 15 mph | 308 kcal/h 86 W | 959 kcal/h | 915 kcal/h | 786 kcal/h 10 METs |
| 18 mph | 484 kcal/h 135 W | 1370 kcal/h | 1213 kcal/h | 943 kcal/h 12 METs |
| 21 mph | 723 kcal/h 202 W | 1878 kcal/h | 1573 kcal/h | 1242 kcal/h 15.8 METs |
165 lb rider on a 20 lb road bike on the hoods, paved road, 24% gross efficiency. Activity-table column uses the Ainsworth Compendium bicycling MET values by speed band × 3.5 × kg ÷ 200 per minute — the formula Omni, calculator.net and the rest run.
Why the activity tables get cycling wrong
Look at the 15 mph row. On a flat, calm day the physics says 308 kcal/h; the table says 786 — 155% higher — because its MET values came from studies of mixed real-world riding, hills and stops included, and it can only key on speed. Turn the same 15 mph into a 3% grade and the honest number jumps 197%, to 915 kcal/h, while the table doesn't move at all. Speed is an output of watts, wind, grade and drafting, so a calorie estimate keyed to speed alone can be wrong in either direction by half. If you own a power meter or ride a smart trainer, you've already got the right answer on the screen; if you don't, the "no power meter" mode above at least asks about the hill.
A kilocalorie is 4.184 kJ, so 1,000 kJ of pedaling is only 239 kcal of mechanical work. But muscles are about 24% efficient — the other three quarters of the food energy leaves as heat, which is why you sweat — and 239 ÷ 0.24 is 996 kcal. The ratio is 0.996, so the kJ number on your head unit is the calorie count to within rounding. Individual efficiency runs about 20–25%, which brackets the same 1,000 kJ between 1195 and 956 kcal — still far tighter than any table.
Does a heavier rider burn more calories cycling?
On the flat, barely: at 12 mph a 150 lb rider burns about 178 kcal/h and a 200 lb rider about 198, because most of the work at that speed goes into air, and air doesn't care what you weigh. Point the road up 5% at the same speed and the gap opens to 921 vs 1160 kcal/h — gravity bills by the pound. This is the real version of the "heavier people burn more" line in every table: true on hills, mostly false on the flat, and entirely a matter of watts either way.
Body fat stores roughly 3,500 kcal per pound. At a steady 150 W the pedals burn about 538 kcal an hour — so a pound is about 6.5 hours of steady riding, and the "700 calories an hour" the tables promise a casual rider is usually the calorie count of someone racing. Cycling is a wonderful way to burn energy precisely because you can do a lot of it; it isn't a shortcut, and the post-ride scale is measuring sweat, not fat.
Calories per mile cycling
About 21 kcal per mile for the 165 lb rider at 15 mph on the flat — and it's nearly flat across speeds, because riding faster burns more per hour but covers more miles. The per-mile number rises with hills, headwinds, knobby tires and an upright position, and falls in a paceline, where the rider behind can do 30% less work at the same speed. That's the reason two friends can finish the same group ride with calorie counts that differ by a third, and both be right.
Calories burned vs calories to eat back
The calorie total is a good guide to recovery meals and a poor guide to on-bike eating. During the ride your body draws on fat for a big share of the energy — most of it at endurance pace — so the number you need to replace while riding is the carbohydrate portion, which the fueling calculator computes from the same watts. Use this page for the whole-day budget and that one for what goes in the jersey pockets.