Concept2 Calorie Converter
Kilojoules are the everyday energy unit on Australian food labels, yet the ergo is where the conversion suddenly matters. This tool turns PM5 kJ into calories burned, or a calorie goal into a kJ target, all on the official Concept2 formula.
Last verified: 17 May 2026
How do you convert Concept2 kJ to calories?
The official conversion is: calories per hour = (kJ per hour x 4) + 300. Multiplying by 4 reflects the body's roughly 25% mechanical efficiency, and the +300 covers the metabolic cost of simply being alive and working. Multiply that hourly rate by your session length in hours for the total. Row 240 kJ in 30 minutes on the ergo and you have burned 1,110 kcal.
Enter your session
The kJ total on the monitor when you finish the piece.
The calorie total you are aiming to burn this session.
Context
- Per-hour rate:
- kJ rate:
- Per kg body weight:
- Food equivalent:
The Concept2 formula is built on population averages. Your own burn shifts with fitness, body composition, training background and metabolism, so read the result as a solid estimate rather than a lab measurement.
Common session calorie totals
Figures below come straight from the Concept2 formula, applied to common ergo sessions held at constant wattage.
| Session | kJ | Calories | Rate |
|---|---|---|---|
Worked example
Setup: A 30-minute steady state on the ergo ends with 240 kJ showing on the PM5. What was the calorie burn?
kJ per hour = 240 / 0.5 = 480
Calories per hour = (480 × 4) + 300 = 2,220 kcal/hr
Session total = 2,220 × 0.5 = 1,110 kcal
The per-hour figure of 2,220 kcal/hr sits well above the session total because only half an hour of the +300 baseline is counted. Stretch the same wattage over a longer session and that baseline thins out across the extra time, which is why short sharp pieces always look calorie-dense for their length.
How the Concept2 calorie formula works
The formula
Every ergometer Concept2 makes uses the same published equation: calories per hour = (kJ per hour x 4) + 300. Multiplying kJ by 4 turns flywheel work into total energy cost, because the human engine runs at roughly 25% mechanical efficiency - around 4 kcal of food energy buys 1 kJ of measurable work. The +300 is a flat hourly allowance for your metabolism, added regardless of effort. Whole-session totals follow the same shape: total kcal = (total kJ x 4) + (300 x hours).
Why does the formula add 300 calories per hour?
Even parked on the ergo doing nothing, your body is spending energy. An adult of about 80kg uses 60-80 kcal an hour at rest keeping the heart, brain and body temperature ticking over. Concept2 settled on 300 kcal/hr as the extra allowance once you are actually training: resting metabolism plus harder breathing, postural work on the slide, grip, and muscle heat. It is less a baseline than the running cost of exercising.
Why does session length change the number?
The +300 accumulates by the hour, which is why time matters. Ten minutes at 240 W delivers 144 kJ: work calories 144 x 4 = 576 kcal, baseline 300 x (1/6) = 50 kcal, giving 626 kcal. Hold that same 240 W for sixty minutes and you produce 864 kJ, collect the full 300 baseline kcal, and finish on 3,756 kcal. Both parts grow linearly with time, but the baseline stands out most on short efforts, where it inflates the per-hour rate.
Is this accurate?
As a population average, yes. Concept2 built the formula from VO2 testing on typical adult ergometer users, so an individual rower can sit 10-20% either side of it depending on weight, body composition, training history and metabolic efficiency. The monitor only ever sees wattage, never the person. Plan nutrition off it as an estimate, and if you want a second angle on the effort, run your numbers through the erg pace calculator or the watts to split converter.
For cross-sport comparisons, the rowing to running converter puts erg pace in road-running terms. The VO2 max calculator reads capacity off a hard piece, and calorie-target sessions sit ready in the erg workout library.
Frequently asked questions
Why is there a flat 300 kcal per hour in the formula?
Because kJ x 4 only accounts for energy that reached the flywheel. While you row you are also breathing hard, pumping blood, holding posture and generating heat, and none of that shows up as work on the monitor. Concept2 measured typical adult rowers with VO2 testing and settled on 300 kcal/hr to cover that exercising overhead. Nothing free about it - it is what the body spends around the strokes.
How close will the calorie estimate be for me?
Expect roughly 10-20% of slack either way. The formula was fitted to an average adult, and it ignores body weight entirely - a 60kg lightweight and a 100kg heavyweight holding identical wattage get identical numbers, even though the heavier rower genuinely burns more. Training background and body composition move the real figure too. Use it to plan, not to audit.
Does drag factor change calories burned?
Wattage and time are the only inputs, so no. Set the ergo to drag 130 or drag 110 and hold 250 W for 30 minutes either way - the PM5 reports the same calories in both cases. Drag changes the feel of the load, the rating you drift toward and which muscles tire first, but the calorie figure is a pure record of work done.
My Garmin says something different to the PM5. Which is right?
Back the PM5. It measures work at the flywheel and adds the fixed baseline, while a watch reverse-engineers calories from heart rate, age, sex and weight. Heart rate is a leaky proxy - coffee before training, a warm shed, or plain nerves before a state championship ergo test all push it up without burning extra energy. Work-based beats inferred for erg sessions.
Can I use the calorie figure for weight management?
Treat it as the ceiling of your likely burn and log food intake alongside it. Change shows up over weeks of consistent training, not from any single session, so the noise in one readout washes out. Weekly volume across the season - through winter ergo blocks and into Head of the Yarra preparation - and consistent eating decide the outcome, not whether one row logged 1,100 or 1,300 kcal.
Sources & references
- Concept2: Calorie Calculator (official formula reference) — Concept2 Inc.
- Concept2: Calories Burned and Calorie Pace on the Performance Monitor — Concept2 Inc.
- Concept2: Watts Calculator (power-to-pace reference) — Concept2 Inc.
- Hagerman, F. (1984). Applied physiology of rowing. — Sports Medicine
- Smith, T. & Hopkins, W. (2012). Measures of rowing performance. — Sports Medicine
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