Concept2 Calorie Converter
Take the kJ number off your PM5 and turn it into total calories burned - or run it the other way and find the kJ target that hits your calorie goal. Runs the official Concept2 formula. No spreadsheet needed.
Last verified: May 17, 2026
How do you convert Concept2 kJ to calories?
Concept2 uses a single published formula for every ergometer they sell: calories per hour = (kJ per hour x 4) + 300. The x4 factor reflects roughly 25% mechanical efficiency - your body burns around 4 kcal of energy to push 1 kJ of work into the flywheel. The +300 is an active metabolic baseline that runs whether you are putting out 300 watts or barely paddling. To get a session total, multiply the per-hour calorie rate by your session length in hours. A 30-minute piece producing 240 kJ works out to 1,110 kcal total - the same figure your PM5 calories screen shows. This calculator lets you verify that number or find the kJ output needed to hit a specific calorie 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 step off the erg after a 30-minute steady-state session and the PM5 reads 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
The per-hour rate (2,220 kcal/hr) looks high compared with the session total because the +300 baseline gets divided across just half an hour. Longer sessions spread that baseline across more time, which is why the per-hour rate looks more reasonable on a 60-minute row than on a 10-minute interval.
How the Concept2 calorie formula works
The formula
Concept2 applies one calorie formula to every ergometer in their lineup: calories per hour = (kJ per hour x 4) + 300. The x4 multiplier converts mechanical output (kJ reaching the flywheel) into total metabolic cost, built on the observation that the human body operates at roughly 25% mechanical efficiency - about 4 kcal of food energy is consumed for every 1 kJ delivered as work. The +300 is a constant active metabolic baseline that applies at any effort level. To find total calories for a session of any length: total kcal = (total kJ x 4) + (300 x hours).
Why does the formula add 300 calories per hour?
Your body does not stop burning fuel just because you are moving slowly. A typical 80kg adult uses 60-80 kcal per hour at complete rest to keep the heart beating, the brain running and core temperature stable. Concept2 pegged 300 kcal/hr as the appropriate active baseline for someone exercising on the erg - it accounts for resting metabolism plus the elevated costs of maintaining posture on the slide, breathing against resistance, and the thermal load from working muscles. It is not padding - it is what your physiology costs during a training session.
Why does session length change the number?
The +300 accrues per hour. Take a 10-minute interval at 240 W: the flywheel absorbs 144 kJ of work. Work calories: 144 x 4 = 576 kcal. Baseline: 300 x (1/6) = 50 kcal. Session total: 626 kcal. Run the same 240 W for a full hour: 864 kJ of work, 300 kcal baseline, 3,756 kcal total. The work component and the baseline both scale linearly with time, but on a short piece the baseline dominates the per-hour rate and makes it look large relative to what you actually held.
Is this accurate?
It is accurate as a population average. Concept2 grounded the formula in VO2 measurements from representative adult ergometer users. For any individual rower, real calorie burn may differ by 10-20% in either direction based on body weight, lean mass, training history and metabolic efficiency. The PM5 does not know who you are - it knows your wattage. For training planning, treat the output as a reliable estimate. To cross-check your effort level, use the erg pace calculator or the watts to split converter to confirm what wattage you actually sustained.
Frequently asked questions
Why does the Concept2 formula include 300 kcal per hour even when you are barely working?
That 300 represents the metabolic overhead of exercising, not just moving the handle. The kJ x 4 component captures only the energy that went into the flywheel. Your body is simultaneously breathing harder, circulating blood at elevated rate, maintaining core temperature and running all the involuntary systems that never switch off. Concept2 established 300 kcal/hr as the active baseline through VO2 testing on typical adult rowers. It is not a freebie - it is the cost your body incurs just by being on the erg.
Is this calorie estimate accurate for me specifically?
It should land within 10-20% for most trained rowers. The formula is calibrated to a population mean, not to you personally. The variable it ignores most significantly is body weight - a 60kg masters rower at Star Boating Club in Wellington and a 100kg openweight rower at West End Rowing Club in Auckland doing identical wattage will have genuinely different calorie burns, but the formula treats them the same. Body composition and training history also shift the real number. Treat the output as a solid planning estimate rather than a precise measurement.
Does drag factor change calories burned?
Not at the same wattage. The Concept2 calorie formula depends only on kJ output and session duration - drag factor, stroke rate and handle technique are invisible to it. Rowing 250 W for 30 minutes at drag 130 produces the same PM5 calorie figure as rowing 250 W for 30 minutes at drag 110. What drag does affect is how that 250 W feels, what stroke rate you naturally settle at, and which muscles accumulate fatigue. The calorie display is purely a function of mechanical work done.
Why is the heart-rate calorie estimate on my watch different from the PM5 number?
The two methods measure completely different things. The PM5 reads mechanical work directly from flywheel physics and adds the 300 kcal/hr baseline. A sports watch estimates calories by linking heart rate to energy expenditure using formulas derived from cardio studies - a less direct measurement that is easily inflated by stress, caffeine or dehydration. For rowing, the PM5 number is generally more accurate because it is grounded in actual power output rather than a physiological proxy.
Should I trust the calorie display for fat loss planning?
As a planning input yes, as a precise ledger no. If you are working toward a calorie deficit, use the PM5 figure as a reasonable ceiling on likely burn and pair it with consistent food tracking. Fat loss over a season at a New Zealand club is determined by cumulative weekly volume and food intake, not by the accuracy of any single session readout. The noise in one session evens out across weeks - what matters is the pattern.
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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