Cycling calorie
calculator

Calories burned cycling from your average power and ride time — the power-meter method: kilojoules of work divided by gross efficiency. With the efficiency band the "1 kJ ≈ 1 kcal" rule hides, and why the number doesn't depend on your bodyweight.

How the math works

Two steps, and the first is the honest one. A power meter integrates your power over time and reports the mechanical work you did, in kilojoules. That is a measurement, not a guess: a watt is one joule per second, so watts times seconds is joules.

The second step is where the uncertainty lives. Your body spends more chemical energy than the work that reaches the pedals; gross efficiency is the fraction that gets there, and for cycling it runs about 20–25% (Allen & Coggan 2019). Because 1 kcal = 4.184 kJ, kilojoules of work equal kilocalories burned exactly at a gross efficiency of 1 / 4.184 = 23.9% — which is the whole basis of the popular "1 kJ ≈ 1 kcal" shortcut. It's a convenient coincidence, not a law, and it assumes you sit at the efficient end of the range.

Worked example

A rider holds an average of 200 W for 1 hour. Power (watts), work (kJ) and energy (kcal) are the same numbers in any unit system; only the optional watts-per-kilogram uses bodyweight.

• Work: 200 W × 3,600 s / 1,000 = 720 kJ
• Calories (1 kJ ≈ 1 kcal): 720 kcal — because the rule assumes 23.9% efficiency
• The efficiency band: at 25% efficiency it's 688 kcal (720 / 1.046); at 20% it's 860 kcal (720 / 0.8368). So the honest answer is ≈688–860 kcal, with the tidy 720 near the low end
• Same ride, three riders: a 132 lb (60 kg), a 165 lb (75 kg), and a 198 lb (90 kg) rider all averaging 200 W for the hour do the same 720 kJ and burn ≈720 kcal each. Only their W/kg differs — 3.33, 2.67, and 2.22 W/kg

That last line is the part most calculators get wrong. Calories from power depend on the work you did and how efficiently you did it — not on your bodyweight. A heavier rider needs more power to hold the same speed, but at the same power the calorie cost is the same.

When this calculator is wrong

A power meter is the only exercise-calorie estimate that measures the work instead of guessing it — every speed-based tool infers effort from how fast you went, which wind, gradient, and drafting dominate, so two rides at "15 mph for an hour" can differ nearly twofold in real work. But the last step still divides by an efficiency you don't know. Measured cycling gross efficiency runs about 20–25% (Coyle et al. 1992 found 18.3–22.6% in trained cyclists; Moseley & Jeukendrup 2001 found ~20%), so the same 720 kJ ride is 688 kcal at 25% but 860 kcal at 20% — and the tidy "1 kJ = 1 kcal" answer (720) sits near the low end. The honest output is a band, not a single number.

• The 1:1 rule reads a bit low for most riders. It assumes 23.9% efficiency, but the peer-reviewed measurements cluster nearer 20%, where the same work costs about 20% more calories. If you want a single number, the 22% option is closer to the measured centre than the 1:1 rule.
• It needs a power meter. This is the mechanical work you actually produced. Without a power meter, a "cycling calories" number is inferred from speed and is a much looser estimate — this tool can't rescue that.
• Average power, not normalized power. Use your ride's straight average watts for the work figure. Normalized/weighted power is a training-stress construct, not the actual energy, and using it here overstates the kilojoules.

What to do with the result

Use the kilojoules as the stable number and the calories as a band. If you're eating to fuel or to lose weight, plan against the middle-to-upper part of the range rather than the tidy 1:1 figure — for a 720 kJ ride that's closer to 780 kcal at ~22% efficiency than the 720 the rule prints. Under-fuelling a long ride is the more common and more costly mistake than over-counting it.

For tracking your own training, pick one efficiency and keep it. Gross efficiency is stable within a person — Moseley & Jeukendrup (2001) measured a within-rider variation of only about 2% — so a fixed conversion tracks week-to-week change honestly even if the absolute calorie count is a little off. And if you're comparing riders or judging climbing, the number that matters is W/kg, not raw watts or calories; a 200 W hour is a different effort for a 60 kg rider (3.33 W/kg) than a 90 kg rider (2.22 W/kg) even though the calories match.

Common questions

Do kilojoules equal calories on a bike?

Almost, and by coincidence. Because 1 kcal = 4.184 kJ, kilojoules of work equal kilocalories burned exactly at a gross efficiency of 1/4.184 = 23.9%. Human cycling efficiency runs about 20–25%, so the "1 kJ ≈ 1 kcal" rule is close — but it sits at the efficient end. At a more typical 20–22% efficiency you actually burn 10–20% more than the kilojoule number.

How many calories does an hour of cycling burn?

It depends on the power, not the time alone. At 200 W for an hour that's 720 kJ, so about 720 kcal by the 1:1 rule and roughly 688–860 kcal across the 25%–20% efficiency band. An easy hour at 120 W is 432 kJ (~430–515 kcal); a hard hour at 280 W is 1,008 kJ (~965–1,205 kcal). Power sets the number.

Does bodyweight change the calories?

No — not for a given power. Calories from a power meter depend only on the work you did and your efficiency, so a 60 kg and a 90 kg rider who both average 200 W for an hour burn about the same 720 kcal. Bodyweight only changes watts per kilogram (3.33 vs 2.22 W/kg here). This is the opposite of a treadmill or MET estimate, where calories scale directly with bodyweight.

Which gross efficiency should I use?

For a single planning number, 22% is closer to the measured centre (Coyle 1992: 18.3–22.6%; Moseley & Jeukendrup 2001: ~20%) than the 1:1 rule's implied 23.9%. For tracking your own rides over time, the exact value matters less than picking one and staying consistent, because efficiency is stable within a person.

Should I use average power or normalized power?

Average power. The work done — and therefore the calories — is the true average watts times the time. Normalized (weighted) power is a training-stress metric that weights hard surges more heavily; it's useful for judging how taxing a ride was, but it overstates the actual energy if you plug it in here.

Is a power-based calorie estimate more accurate than a speed-based one?

Its effort term is, by a lot. A power meter measures the work you produced; a speed-based tool guesses it from pace, which wind, hills, and drafting dominate. The one remaining uncertainty in the power method is the efficiency factor — a roughly ±10% band around the middle — which is far tighter than the error in inferring effort from speed.