Concept2 Calorie Converter
Read the work behind your PM5 calorie total. Convert a finished kJ result, or reverse the equation to set a work target for an NCAA program, masters practice, or CrossFit session.
Last verified: May 17, 2026
How do you convert Concept2 kJ to calories?
Concept2 calculates calories per hour = (kJ per hour x 4) + 300. The x4 reflects roughly 25% mechanical efficiency: producing 1 kJ at the flywheel costs about 4 kCal. The +300 represents active baseline metabolism. Scale that hourly rate to the session length. A 30-minute piece producing 240 kJ equals 1,110 kcal total. Use the calculator to check the PM5 result or reverse the equation from a calorie target.
Enter your workout
The kJ figure displayed at the end of your piece.
How many calories you want to burn in the workout.
Context
- Per-hour rate:
- kJ rate:
- Per kg body weight:
- Food equivalent:
Concept2 built this equation from average VO2 test data. Fitness, body composition, training history, and metabolism change an individual's actual energy use. Plan with the result, but do not treat it as a direct measurement.
Common workout calorie totals
Reference totals use the Concept2 equation and steady power for common erg sessions. Pace conversions assume drag 130.
| Workout | kJ | Calories | Rate |
|---|---|---|---|
Worked example
Setup: After a 30-minute steady-state row, your PM5 reports 240 kJ. What calorie total does the equation produce?
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 hourly rate (2,220 kcal/hr) looks much larger than the session total because only half of the +300 baseline applies. Short HIIT-style pieces therefore appear efficient for their duration, while a long aerobic row spreads the +300 contribution across more time.
How the Concept2 calorie formula works
The formula
Every Concept2 ergometer uses calories per hour = (kJ per hour x 4) + 300. With roughly 25% mechanical efficiency, the x4 multiplier estimates the food energy needed to deliver work to the flywheel: about 4 kcal burned for each 1 kJ produced. The fixed +300 represents active baseline metabolism. For any session length, apply total kcal = (total kJ x 4) + (300 x hours).
Why does the formula add 300 calories per hour?
Energy use continues between drives. A roughly 175lb adult burns 60-80 kcal per hour at complete rest through circulation, brain activity, and temperature control. Concept2 uses 300 kcal/hr for the extra cost of active exercise, including posture, ventilation, grip, and muscle heat. In this equation, "baseline" means the body's ongoing cost while working, not calories created by the monitor.
Why does workout length change the number?
The +300 applies by the hour. During a 10-minute interval at 240 W, you put 144 kJ into the flywheel. Work contributes 144 x 4 = 576 kcal, while baseline adds 300 x (1/6) = 50 kcal. Total = 626 kcal. Hold the same 240 W for an hour and the machine records 864 kJ of work, adds 300 baseline kcal, and reaches 3,756 kcal. Both parts scale with time.
Is this accurate?
It is useful at the population level. Concept2 based the equation on VO2 tests from typical adult erg users. An individual result may vary 10-20% either way because the monitor sees work, not body weight, composition, training history, or metabolic efficiency. Use it as a nutrition estimate. Confirm the power behind the session with the erg pace calculator or watts to split converter.
Compare erg and road effort in the rowing to running converter. Estimate aerobic capacity from a test in the VO2 max calculator, or choose a calorie-target session from the erg workout library when your gym programs by energy output.
Frequently asked questions
Why does the Concept2 formula include 300 kcal per hour even when you barely work?
That 300 estimates active baseline metabolism during exercise. The mechanical term (kJ x 4) accounts only for energy delivered to the flywheel. Breathing, circulation, muscle temperature, and involuntary processes still require fuel during an easy row. Concept2 fixed the addition at 300 kcal/hr after VO2-based testing with typical adult rowers. It represents the cost of keeping the body working, not a bonus from the monitor.
Is this calorie estimate accurate for me specifically?
Expect possible variation of 10-20% in either direction. The equation comes from group averages and does not adjust for body size. A 130lb athlete and a 220lb athlete can produce the same wattage while using different total energy. Training history, body composition, and metabolic efficiency add more variation. Use the output for planning, not as a medical measurement.
Does drag factor change calories burned?
Not when wattage stays constant. Concept2 uses kJ (or watts) and time, not drag factor, stroke rate, or handle position. Drag 130 at 250 W for 30 minutes produces the same PM5 calorie total as drag 110 at 250 W for 30 minutes. The load may feel different and alter your natural rate or fatigue, but equal work gives equal displayed calories.
Why is the calorie number on my Apple Watch or Garmin different from the PM5?
The devices start with different data. A PM5 measures mechanical work at the flywheel and adds the +300 baseline. A wrist device infers energy use from heart rate, age, sex, and weight. Caffeine, dehydration, and room temperature can change pulse without matching changes in work. For rowing, the PM5 usually has the stronger input because it records output directly.
Can I trust the calorie display for fat loss or weight management?
Use it as a planning estimate, not an exact credit against food. For a calorie deficit, treat the PM5 total as an upper bound and record intake consistently. Bodyweight trends develop across weeks, which reduces the importance of error in one workout or watch reading. Diet consistency and weekly training volume matter more than whether one row reports 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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