Concept2 Calorie Converter
Finish the erg, note the kJ, and let this converter tell you the calorie cost - or flip it around and get the kJ target that matches a calorie goal. Built on the official Concept2 formula, handy through the long winter erg blocks between regatta seasons.
Last verified: May 17, 2026
How do you convert Concept2 kJ to calories?
Use the Concept2 equation: calories per hour = (kJ per hour x 4) + 300. The x4 exists because rowing bodies are about 25% efficient, so each kJ of flywheel work costs near 4 kcal. The +300 is your hourly metabolic overhead while training. Scale the hourly rate by session hours: 240 kJ across 30 minutes comes to 1,110 kcal.
Enter your session
Whatever the monitor shows for kJ once the piece is done.
Your calorie goal for the erg session.
Context
- Per-hour rate:
- kJ rate:
- Per kg body weight:
- Food equivalent:
Concept2 fitted this formula to an average adult, so individual results drift with fitness, build, training history and metabolism. It is a dependable estimate, not a measurement of you personally.
Common session calorie totals
Session totals below apply the Concept2 formula to standard erg pieces rowed at even wattage.
| Session | kJ | Calories | Rate |
|---|---|---|---|
Worked example
Setup: The PM5 reads 240 kJ after a 30-minute steady-state erg. What did it cost in calories?
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
That 2,220 kcal/hr rate dwarfs the 1,110 kcal total for a simple reason: the half-hour piece only earns half of the +300 hourly baseline, yet the rate expresses everything per full hour. On longer rows the baseline spreads thinner and the hourly figure settles down.
How the Concept2 calorie formula works
The formula
One equation covers the whole ergometer range: calories per hour = (kJ per hour x 4) + 300. Behind the x4 sits the fact that humans convert food to flywheel work at about 25% efficiency, meaning close to 4 kcal in for every 1 kJ out. Behind the +300 sits your metabolism, charged at a flat hourly rate however hard or easy the rowing is. Session totals follow directly: total kcal = (total kJ x 4) + (300 x hours).
Why does the formula add 300 calories per hour?
Metabolism never clocks off. At complete rest an 80kg adult still gets through 60-80 kcal an hour on heartbeat, brain function and staying warm. On the erg those costs rise - posture on the slide, heavier breathing, grip, muscle heat - and Concept2 priced the whole lot at a flat 300 kcal/hr for an exercising adult. Think of it as the standing charge of a training session, paid on top of the work you put through the flywheel.
Why does session length change the number?
Time feeds the +300 term. A 10-minute effort at 240 W banks 144 kJ, which converts to 576 kcal of work plus a 50 kcal baseline share (300 x 1/6), totalling 626 kcal. Keep 240 W going for the full hour and the sums become 864 kJ, 3,456 work kcal, the whole 300 baseline, and 3,756 kcal overall. Everything scales with duration, but the baseline is most visible on short pieces because it props up the hourly rate.
Is this accurate?
For the average adult tested in Concept2's VO2 work, yes. For you, allow 10-20% either way - weight, lean mass, training years and metabolic efficiency all move the true figure, and the PM5 sees none of them, only watts. That still makes it a sound base for nutrition planning. Cross-check the effort side with the erg pace calculator or the watts to split converter to confirm the wattage you held.
Related conversions: erg pace to road pace in the rowing to running converter, aerobic capacity in the VO2 max calculator, and structured calorie-target pieces in the erg workout library.
Frequently asked questions
What is the 300 kcal per hour actually paying for?
Everything the flywheel cannot see. The kJ x 4 term records mechanical work alone, while your lungs, heart, core temperature and involuntary systems keep drawing energy the whole time you row. Concept2 ran VO2 testing on typical adult rowers and fixed that exercising overhead at 300 kcal/hr. The figure is a genuine cost, not a bonus.
Will the number match my actual burn?
Within about 10-20% for most people. The equation describes an average adult and never asks your weight, so a 60kg schools rower training for the Maadi Cup and a 100kg club heavyweight at the same wattage receive the same readout despite different real burns. Build and training history matter too. It is a planning figure, and a good one, but not a personal measurement.
Does changing drag factor change the calories?
No - the formula only reads work and time. Hold 250 W for 30 minutes and the calorie result is identical whether the drag sits at 110 or 130. What the drag setting alters is stroke feel, natural rating and where fatigue lands first. Since the monitor counts pure mechanical output, the calorie line ignores all of that.
The watch on my wrist disagrees with the PM5. Why?
Different measurement philosophies. The erg counts real work at the flywheel and adds the fixed hourly baseline; the watch guesses energy from heart rate combined with your age, sex and weight. Heart rate wanders for reasons that burn nothing extra - caffeine, dehydration, race-day nerves at Lake Karapiro - so for erg work the PM5 is the more trustworthy of the two.
Is the calorie readout good enough for losing weight?
Good enough to plan with, provided you treat it as an upper bound and track food honestly beside it. One session's error is irrelevant; weeks of them average out. What decides body composition for a Kiwi club rower over a season is total training volume and consistent eating, not the couple of hundred kcal of uncertainty in any single erg.
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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