The finding. At the same split, the Concept2 monitor shows every rower the same calories: about 997 Cal per hour at 2:00 per 500 m, whether you weigh 130 lb or 220 lb. Concept2's own correction for body weight moves that figure by a flat 77 Cal per hour for each 45 lb away from 175 lb. That is a 7.7% correction at a 2:00 split but 11.7% at 2:30, so the slower you row, the more your weight matters. And because power rises with the cube of speed, going from 2:00 to 1:50 (9.1% faster) takes 29.8% more watts.
The formula behind the number on the screen
The monitor works in two steps. First it turns your split into power. Concept2 publishes that conversion on its watts calculator page: watts = 2.80 / pace cubed, where pace is seconds per metre. Then it turns power into calories with this formula:
Cal per hour = 4 x 0.8604 x watts + 300
The source for that second step needs a careful label. It is not on the concept2.com pages I fetched. It appears in a thread on the Concept2 forum, where a user quotes the Physics of Rowing page and a statement attributed to Jon Williams of Concept2 (12 August 2004) that the 300 per hour background figure is Concept2's approximation. The form given there is E = (4W + 0.35t) / 4.2 kcal, with W the work in kilojoules and t the time in seconds. Worked out per hour, that is the formula above. So read it as the monitor's convention, reported by Concept2 staff, rather than a published Concept2 specification.
The rowing calorie calculator runs both steps for any split or wattage and shows the arithmetic under the result.
What the 4 and the 300 are, arithmetically
The 0.8604. One watt held for an hour is 3,600 joules. A kilocalorie is 4,184 joules, so one watt-hour is 3,600 / 4,184 = 0.8604 kcal. This part is a pure unit conversion.
The 4. Multiplying the mechanical work by 4 says your body spends four units of energy for every unit that reaches the handle. That is the same as assuming 25% efficiency (1 / 4). Together, 4 x 0.8604 = 3.44 Cal per hour for each watt. In the forum form the divisor is 4.2 rather than 4.184, which gives 4 x 3.6 / 4.2 = 3.43: the same thing, rounded differently.
The 300. In the forum form this is 0.35 kJ every second. Over an hour that is 0.35 x 3,600 / 4.2 = 300 kcal. It does not depend on how hard you pull: a rower holding a 2:30 split and one holding 1:45 both get the same 300 per hour. Expressed as power, 300 kcal per hour is a steady 349 W of heat.
It is tempting to call the 300 "resting metabolism", but the arithmetic says it is larger than that. Spread over a 175 lb (79.4 kg) body, 300 kcal per hour is 3.78 kcal per kilogram per hour. The Compendium of Physical Activities defines 1 MET, the resting rate, as 1 kcal per kilogram per hour, so the background figure is close to four times a resting rate for that weight. Concept2 staff described it only as an approximation, and I have found no published breakdown of what it is meant to include, so I will not guess.
Where your weight enters, and where it does not
The monitor never asks your weight. Concept2's calorie calculator page gives the correction:
True Cal per hour = monitor Cal per hour - 300 + 1.714 x weight in pounds
Look at what this does. 1.714 x 175 = 300, so for a 175 lb rower the correction cancels and the monitor is already "right". For anyone else, the correction swaps the fixed 300 for a figure that grows with weight. The work term, 3.44 Cal per hour per watt, is left alone: the same split means the same watts, and the formula charges the same energy for that work at any body weight.
So the correction is a flat 1.714 Cal per hour per pound. A 130 lb rower is 45 lb under 175 and loses 77 Cal per hour; a 220 lb rower is 45 lb over and gains 77. Here is what that looks like across common splits:
| Split /500 m | Watts | Monitor Cal/hr (any weight; fits 175 lb) | 130 lb | 220 lb | Correction (77 Cal/hr) as share of monitor |
|---|---|---|---|---|---|
| 1:45 | 302.3 | 1,341 | 1,263 | 1,418 | 5.8% |
| 1:50 | 263.0 | 1,205 | 1,128 | 1,282 | 6.4% |
| 2:00 | 202.5 | 997 | 920 | 1,074 | 7.7% |
| 2:10 | 159.3 | 848 | 771 | 925 | 9.1% |
| 2:15 | 142.3 | 790 | 712 | 867 | 9.8% |
| 2:30 | 103.7 | 657 | 580 | 734 | 11.7% |
The last column is the finding in numbers. The weight correction is the same 77 Cal per hour on every row, but the monitor figure it is compared with shrinks as the split slows. At 1:45 the correction is 5.8% of the screen number; at 2:30 it is 11.7%. A light rower on an easy steady-state piece sees the largest overstatement, a heavy rower on the same piece the largest understatement.
For a 30-minute piece at 2:00, the monitor shows about 499 Cal. Corrected, that is about 460 for a 130 lb rower and 537 for a 220 lb rower. At 2:30 the monitor shows about 328, against 290 and 367.
The cube law: why 10 seconds costs so much
Watts = 2.80 / pace cubed. A 2:00 split is 120 / 500 = 0.24 seconds per metre, and 2.80 / 0.24 cubed = 202.5 W. A 1:50 split is 0.22 seconds per metre, and 2.80 / 0.22 cubed = 263.0 W.
So taking 10 seconds off a 2:00 split means 60.4 more watts, 29.8% more power, for a boat speed that is only 9.1% higher (120 / 110 = 1.091). The cube makes the ratio easy to check by hand: 1.091 cubed = 1.298. Near 2:00, each second off the split costs about 5.1 W. To double your power from 2:00 you would need a split of about 1:35.2.
The calories on the monitor rise less steeply than the watts, because the 300 stays put: from 2:00 to 1:50 the screen goes from 997 to 1,205 Cal per hour, 20.9% more, while power rose 29.8%.
Per 2,000 m, faster costs more (unlike running)
On flat ground, the ACSM running equation gives the same net calories per mile at any speed (the arithmetic is in does running faster burn more calories per mile?). The rowing monitor behaves differently. Work per metre is watts x seconds per metre, which is 2.80 / pace squared, so it rises as you go faster. The background part does the opposite: a slower piece takes longer, so it collects more of the fixed 300 per hour.
| Split /500 m | 2,000 m time | Work part (Cal) | Background part (Cal) | Monitor total (Cal) |
|---|---|---|---|---|
| 1:45 | 7:00 | 121.4 | 35.0 | 156.4 |
| 1:50 | 7:20 | 110.6 | 36.7 | 147.3 |
| 2:00 | 8:00 | 92.9 | 40.0 | 132.9 |
| 2:10 | 8:40 | 79.2 | 43.3 | 122.5 |
| 2:20 | 9:20 | 68.3 | 46.7 | 115.0 |
| 2:30 | 10:00 | 59.5 | 50.0 | 109.5 |
The work column at 1:50 is 1.86 times the work column at 2:30, which is (150 / 110) squared. On the monitor, a 2,000 m test at 1:50 counts about 147 Cal; the same distance at 2:30 counts about 110. If you row a fixed distance, the monitor credits the fast piece with more energy; if you run a fixed distance, the running equation does not.
The same watts on a bike and in the Compendium
The site's stationary bike calorie calculator uses two methods: the ACSM leg cycling equation and a work method at 20% gross efficiency (research summarised in Sports Medicine Open, 2019, puts cycling gross efficiency mostly around 18 to 20% at 150 W). For 30 minutes at 150 W, a split of about 2:12.6 on the rower:
- Rowing monitor: about 408 Cal, built from 258 Cal of work (at 25% efficiency) plus 150 Cal of background.
- Rowing monitor corrected for 160 lb: about 395 Cal.
- Bike, work method at 20%: about 323 kcal.
- Bike, ACSM leg cycling equation at 160 lb: about 318 kcal.
The rower's work part is actually smaller than the bike's, because 25% efficiency charges less energy per watt than 20%. The rower comes out higher only because of the 150 Cal background added on top. The 2024 Compendium, used by the calories burned calculator, lists stationary rowing at 150 to 199 W (code 02073) at 11.0 METs, which for 30 minutes at 160 lb is about 411 kcal, close to the monitor's 408 at 150 W. At 100 to 149 W (02072, 7.5 METs) it is about 280 kcal.
Which number to trust
None of these is a measurement of you. The monitor formula is a fixed convention with a single efficiency and a single body weight; the weight correction fixes the second assumption, not the first. Technique, stroke rate and fitness change how much energy a given split costs a particular person, and other brands of rowing machine use their own formulas, so their screens will not match. If you log rowing next to running or cycling, the most consistent choice is the weight-corrected figure, which the calculator shows as the main result when you enter your weight. These are energy estimates, not a weight-loss forecast.
If you want to see how the Compendium's MET values compare across activities, METs explained works through them.
Sources: Concept2 watts calculator; Concept2 calorie calculator (body-weight adjustment); Concept2 forum thread quoting the monitor calorie formula; Herrmann et al. (2024), 2024 Adult Compendium of Physical Activities, conditioning exercise; Matomäki, Linnamo and Kyröläinen (2019), cycling mechanical efficiency, Sports Med Open. Rules checked . Found a problem? Tell us.
Questions
Does the rowing machine count calories based on weight?
No. The Concept2 monitor uses one formula, 4 x 0.8604 x watts + 300 per hour, with no weight in it. Concept2's calorie calculator page corrects it: subtract 300 and add 1.714 x your weight in pounds.
How many more watts is a 1:50 split than a 2:00 split?
About 60 W more: 263.0 W against 202.5 W, an increase of 29.8% for a split that is 9.1% faster, because watts = 2.80 / pace cubed.
Are rowing machine calories accurate for a light person?
They overstate. The monitor matches a 175 lb rower; a 130 lb rower burns about 77 Cal per hour less than it shows by Concept2's correction, which is 11.7% of the screen figure at a 2:30 split.
Why does the rower show more calories than the bike at the same watts?
The rower adds a fixed 300 Cal per hour on top of the work. At 150 W for 30 minutes the monitor counts about 408 Cal, against about 323 kcal for a bike at 20% efficiency.