kJ to Calories Calculator
Your power meter measures work in kilojoules (kJ). For cyclists, that number is very close to the calories you burned — enter your ride’s kJ to see roughly how many calories it cost.
Learn About TrainerRoadCalories Burned Cycling
1000 kcal
Literal unit conversion 239 kcal
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Why kJ and Calories Are Roughly 1:1 in Cycling
Here is the part that surprises people: 1,000 kJ of work on the bike burns roughly 1,000 calories — not the 239 you get from a textbook unit conversion. The reason is efficiency. Your body is only about 20–25% efficient at turning food energy into pedal power, so for every kilojoule that reaches the cranks, you burn around four to five kilojoules of metabolic energy. Convert that to calories and the two roughly cancel out — leaving the handy rule of thumb that calories burned ≈ kilojoules of work. It is an approximation, not an exact figure: a less efficient rider can burn up to about 20% more than their kilojoule count, so treat the result as a close estimate.
Your Body Is 20–25% Efficient
For every kilojoule that reaches the cranks, you burn around four to five kilojoules of metabolic energy.
The Math Roughly Cancels
Convert that metabolic energy to calories and the factors nearly cancel — calories burned ≈ kilojoules of work.
A Close Estimate, Not a Lab Test
A less efficient rider can burn up to about 20% more than their kilojoule count, so treat the result as a close estimate.
The Literal Conversion (and Why It Misleads Cyclists)
Strictly as units, 1 kilojoule equals 0.239 calories, so 1,000 kJ is 239 kcal. That is what a generic converter tells you — and it is wrong for a bike ride, because it ignores your body’s efficiency. When you want to know how many calories a ride actually cost, use the cycling rule (≈ 1:1), not the literal conversion.
≈ 1:1 Use this for rides
The cycling rule
Calories burned ≈ kilojoules of work. Your body’s ~20–25% efficiency and the unit conversion roughly cancel out.
1,000 kJ ≈ 1,000 kcal
× 0.239 Misleading for rides
The literal unit conversion
Correct thermodynamics, wrong question — it ignores the metabolic energy your body spent to produce that work.
1,000 kJ = 239 kcal
How to Find Your Kilojoules
Any power meter records total work in kilojoules. You will see it as “Work” or “kJ” in your ride summary on your head unit, in TrainerRoad, or in your analysis app. No power meter? Multiply your average power in watts by your ride time in hours, then by 3.6 — for example, 200 W for two hours is about 1,440 kJ, and therefore roughly 1,440 calories.
These examples come straight from that math — and because of the ~1:1 rule, each ride’s kilojoules are also roughly the calories it burned.
Recovery Spin
Half an hour of easy spinning barely touches your reserves.
30 min 100 W
180 kJ ≈ kcal
Endurance Ride
Steady aerobic riding at a conversational pace.
1 hour 150 W
540 kJ ≈ kcal
Sweet Spot Workout
Structured intervals just below your FTP.
1 hour 200 W
720 kJ ≈ kcal
Group Ride
The worked example from above — 200 W held for two hours.
2 hours 200 W
1,440 kJ ≈ kcal
Long Endurance Ride
Duration piles up energy demands even at an easy pace.
3 hours 180 W
1,944 kJ ≈ kcal
Century Ride
A big day out that demands a real fueling plan.
5 hours 170 W
3,060 kJ ≈ kcal
Make Those Calories Count
Burning calories is a by-product; getting faster is the point. A structured training plan from TrainerRoad turns the work you do into real fitness — and AI FTP Detection keeps your training dialed in without a fitness test.
TrainerRoad is cycling’s most effective training system: structured workouts, science-based plans, and AI that personalizes everything to you — including your FTP.
How AI FTP Detection Works
Connect Your Rides
Import your ride history from Garmin, Strava, Wahoo, and more.
AI Analyzes Every Ride
TrainerRoad AI studies your power data and how your fitness responds to training.
Your FTP, Detected
Accept your new FTP with one tap — every workout adjusts to it instantly.
“AI FTP Detection is seriously amazing and so accurate!”
Real Riders. Real Results.
“It helped me increase my FTP by 40w in 4 months. What else do I need to say?”
“TR has taken me from a Cat 5 to a Cat 1 (pending approval) in about 6 seasons… a 6th place finish at nationals.”
“Just started cycling less than 12 months ago… Started at 195 FTP and with TrainerRoad progression I'm sitting at 272.”
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