Concept2 Calorie Converter
The number the PM5 gives you in kJ becomes a calorie total here, and a calorie goal becomes the kJ you need to row. Everything runs on the official Concept2 formula, whether the winter erg work is happening in Cork, Galway or a shed beside the Liffey.
Last verified: May 17, 2026
How do you convert Concept2 kJ to calories?
Apply Concept2's published equation: calories per hour = (kJ per hour x 4) + 300. Four calories per kilojoule follows from the body's roughly 25% mechanical efficiency, while the +300 charges an hourly metabolic overhead for training. Multiply the hourly figure by your hours rowed: a 30-minute erg producing 240 kJ totals 1,110 kcal.
Enter your session
Read the kJ figure off the monitor when the erg finishes.
The total calories you plan to burn this session.
Context
- Per-hour rate:
- kJ rate:
- Per kg body weight:
- Food equivalent:
Being a population-average formula, the Concept2 number will not match every rower exactly - fitness, build, training years and metabolism all pull it about. A useful estimate, nothing more precise than that.
Common session calorie totals
Typical erg sessions at level wattage, converted through the Concept2 formula.
| Session | kJ | Calories | Rate |
|---|---|---|---|
Worked example
Setup: After a half-hour steady-state erg the PM5 displays 240 kJ. What is the calorie total?
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 2,220 kcal/hr rate reads high next to the 1,110 kcal total. The reason is arithmetic: a 30-minute piece collects just half of the hourly +300 baseline, but the rate is quoted per full hour. Longer outings water the baseline down and the two figures sit closer together.
How the Concept2 calorie formula works
The formula
The same published equation applies to any ergometer Concept2 has built: calories per hour = (kJ per hour x 4) + 300. Work on the flywheel is multiplied by four because human muscle turns food into mechanical output at around 25% efficiency, roughly 4 kcal spent per 1 kJ produced. On top sits the +300, a fixed hourly metabolic charge that applies regardless of intensity. For a full session: total kcal = (total kJ x 4) + (300 x hours).
Why does the formula add 300 calories per hour?
A body at rest is still a furnace on low. Around 60-80 kcal an hour keeps an 80kg adult's heart going, brain fed and temperature held, and the moment you sit on the erg those demands climb - breathing deepens, posture works, the grip engages, muscles shed heat. Concept2 rolled the lot into one flat figure, 300 kcal/hr for an exercising adult, and adds it on top of whatever work the flywheel records.
Why does session length change the number?
Because the baseline is hourly, duration shapes the total. Ten minutes at 240 W is 144 kJ of work: 144 x 4 = 576 kcal, plus a sixth of the baseline (300 x 1/6 = 50 kcal), makes 626 kcal. The same wattage sustained for an hour gives 864 kJ, 3,456 work kcal and the full 300 baseline - 3,756 kcal all told. Short pieces carry a proportionally louder baseline, which is why their per-hour rates look so generous.
Is this accurate?
Yes, at the level of population averages - the formula came out of Concept2's VO2 studies on ordinary adult ergometer users. Any one rower may land 10-20% away from it in either direction, since weight, lean mass, training age and metabolic efficiency never enter the calculation; wattage is all the monitor knows. Sound enough for planning food around training. To verify the effort itself, the erg pace calculator and the watts to split converter confirm the wattage behind your split.
Take the comparison further with the rowing to running converter for road equivalents, the VO2 max calculator for a capacity estimate, and the erg workout library for sessions built on calorie targets.
Frequently asked questions
Where does the extra 300 kcal per hour come from?
From you, not the machine. The kJ x 4 half of the formula covers only flywheel work, yet a rower mid-session is also ventilating hard, circulating blood, holding position and radiating heat. VO2 testing on typical adults let Concept2 price that whole overhead at a flat 300 kcal/hr. It is spent energy in every sense, just energy that never reached the handle.
How accurate is the figure for an individual rower?
Reckon on a 10-20% margin. The equation models an average adult and takes no account of body weight, so a 60kg junior sculler on the Lee and a 100kg senior eight rower in Dublin holding matched wattage are handed the same number, though their true burns differ. Composition and training history widen the gap further. Plan with it; do not treat it as gospel.
Will a different drag factor alter calories burned?
Not while the wattage stays put. Time and kJ are the formula's only ingredients, so 250 W held for 30 minutes yields one calorie figure whether drag is 110 or 130. Drag decides how heavy each stroke feels, the rating you settle into and which muscles complain first - none of which the calorie calculation ever sees.
Why do my watch and the PM5 disagree on calories?
Two unrelated methods. The monitor works from measured flywheel output plus the standard baseline, while a wrist device infers burn from heart rate filtered through age, sex and weight. Since heart rate rises on caffeine, dehydration or pre-race nerves without any extra energy cost, the PM5's work-based figure is the steadier guide for erg sessions.
Can the calorie display guide fat loss?
It can anchor a plan if you take it as the top end of likely burn and keep an honest food log beside it. No single erg decides anything - results emerge from weeks of consistent volume through the Irish winter season, and the scatter in individual readouts cancels out along the way. Consistency at the club, not calorie precision, moves the outcome.
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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