Concept2 Calorie Converter
Turn your PM5 kJ readout into total calories burned, or work backwards from a calorie target to a kJ goal. Uses the official Concept2 formula. Built for Rowing Australia clubs, GPS schools and AIS-pathway athletes.
Last verified: 17 May 2026
How do you convert Concept2 kJ to calories?
Concept2 publishes one formula: calories per hour = (kJ per hour x 4) + 300. The x4 accounts for roughly 25% mechanical efficiency, meaning 1 kJ of work on the flywheel costs about 4 kCal of total energy expenditure. The +300 covers active baseline metabolism. For a finished training session, multiply the per-hour calorie rate by your actual session duration. A 30-minute piece that produces 240 kJ works out to 1,110 kcal total. The PM5 monitor displays this number on the calories screen - this calculator lets you sanity-check it or work the formula in reverse from a nutrition target.
Enter your session
The kJ figure displayed at the end of your row.
How many calories you want to burn in the session.
Context
- Per-hour rate:
- kJ rate:
- Per kg body weight:
- Food equivalent:
This is the Concept2 formula, which is a population average. Actual calorie burn varies with fitness, body composition, training history and metabolic rate. Treat the number as a useful estimate, not a measurement.
Common session calorie totals
Calculated using the Concept2 formula for typical erg sessions at steady wattage.
| Session | kJ | Calories | Rate |
|---|---|---|---|
Worked example
Setup: You finish a 30-minute steady-state piece and the PM5 shows 240 kJ. How many calories did you 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
Notice the per-hour rate (2,220 kcal/hr) is much higher than the session total, because the formula spreads the +300 baseline calories across only half an hour. This is why short pieces look efficient relative to their length and long pieces dilute the +300 across more time.
How the Concept2 calorie formula works
The formula
Concept2 publishes one calorie formula for every ergometer sold: calories per hour = (kJ per hour x 4) + 300. The x4 multiplier converts mechanical work (kJ on the flywheel) into total energy expenditure on the assumption that the human body operates at roughly 25% mechanical efficiency - you have to burn about 4 kcal of food energy to push 1 kJ of work into the flywheel. The +300 is a fixed baseline metabolic rate that the formula adds whether you are rowing or sitting still. For a session of any duration, the total calorie burn is: total kcal = (total kJ x 4) + (300 x hours).
Why does the formula add 300 calories per hour?
Because your body burns calories even when you are not exercising. A roughly 80kg adult burns 60-80 kcal per hour at rest just to keep the heart pumping, the brain firing and the body warm. Concept2 picked 300 kcal/hr as the additional rate for someone actively exercising - it covers your baseline metabolism plus the elevated demands of sitting up, breathing harder, gripping the handle, and the heat produced by the muscles. Calling it just "baseline" undersells it: it is your active resting cost during exercise.
Why does session length change the number?
Because the +300 is per hour. A 10-minute interval at 240 W puts 144 kJ into the flywheel. The work-only calories are 144 x 4 = 576 kcal. The baseline contribution is 300 x (1/6) = 50 kcal. Total = 626 kcal. The same 240 W held for a full hour produces 864 kJ of work, contributes 300 baseline kcal, and totals 3,756 kcal. The work scales linearly with time; the baseline does too, but you notice it more on shorter pieces where it dominates the per-hour rate.
Is this accurate?
It is accurate as a population average. Concept2 derived the formula from VO2 studies of typical adult ergometer users. Your real calorie burn could be 10-20% different in either direction depending on body weight, body composition, training age and individual metabolic efficiency. The formula does not know you exist - it only knows wattage. For nutrition planning, treat the output as a planning estimate. To cross-check against pace, use the erg pace calculator or the watts to split converter to confirm the wattage you actually held during the session.
Frequently asked questions
Why does the Concept2 formula include 300 kcal per hour even when you are barely working?
Because that 300 covers your baseline metabolic cost while exercising. The mechanical work component (kJ x 4) only captures the energy that ended up in the flywheel. You also burn calories breathing, circulating blood, keeping muscles warm and powering involuntary processes - even on the lightest of rows. Concept2 fixed this baseline at 300 kcal/hr after VO2-based testing on typical adult rowers. It is not "free calories" - it is what your body costs to run during exercise.
Is this calorie estimate accurate for me specifically?
Probably within 10-20% either way. The formula is a one-size-fits-all derived from population averages. Body weight is the biggest hidden variable - the formula does not adjust for it, but a 60kg person genuinely burns fewer total calories than a 100kg person doing the same wattage because they carry less mass to fuel. Training age, body composition and metabolic efficiency also matter. Treat the output as an estimate to plan against, not a medical-grade measurement.
Does drag factor change calories burned?
Not at the same wattage. The Concept2 calorie formula depends only on kJ (or watts) and time - not drag factor, stroke rate, or handle position. At drag 130 holding 250 W for 30 minutes, you burn the same calories the PM5 displays as at drag 110 holding 250 W for 30 minutes. What changes is how the load feels, the stroke rate you naturally settle at, and the muscle groups that fatigue first. The calorie number on the monitor is purely a function of work done.
Why is the heart-rate calorie estimate on my Garmin or Apple Watch different from the PM5 number?
They use different methods. The PM5 measures mechanical work (the flywheel cannot lie) and applies the +300 baseline. A wrist-based heart-rate monitor estimates calories from your heart rate, age, sex and weight - which is a much rougher proxy because heart rate spikes for many reasons besides energy expenditure (caffeine, dehydration, anxiety). For rowing specifically, the PM5 figure is usually closer to truth because it is built from work output, not inferred from physiology.
Should I trust the calorie display for fat loss planning?
As a planning estimate yes, as a precise number no. If you are targeting a deficit, treat PM5 calories as the upper bound of likely burn and pair it with a tracked food intake. Real-world fat loss happens slowly across weeks, not session by session - the noise in any individual session calorie figure (yours or your watchs) gets averaged out over time. Bigger drivers of fat loss results are food consistency and total weekly training volume, not whether you burned 1,100 or 1,300 kcal in one row.
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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