Rowing Stroke Power Calculator

The Concept2 Power Formula

The standard rowing ergometer formula converts split time to power output:

P = 2.80 ÷ (t ÷ 500)³

where t is your 500m split time in seconds. This relationship comes from fluid dynamics: the drag force on a rowing shell scales with velocity squared, so power scales with velocity cubed. The constant 2.80 is calibrated to the Concept2 damper setting and drag factor.

At 2:00 per 500m (120 sec): P = 2.80 ÷ 0.24³ = 203 watts. At 1:45 per 500m (105 sec): P = 2.80 ÷ 0.21³ = 302 watts. At 2:30 per 500m (150 sec): P = 2.80 ÷ 0.30³ = 104 watts.

The cubed relationship means small split improvements at fast paces represent much larger power jumps than the same time drop at slow paces. Cutting 10 seconds from a 2:00 split takes you from 203 to 263 watts, a 60 watt gain. Cutting the same 10 seconds from a 2:30 split takes you from 104 to 128 watts, only 24. The faster you already are, the more each second costs.

On-Water vs Ergometer

This formula applies to the erg, and the erg only. On the water, hull drag, blade slip, balance and rigging all enter the picture, and the direction of the difference depends entirely on the boat. In a single scull almost every rower is slower than their erg split, typically by 8 to 10 seconds per 500m. An eight goes the other way and beats the crew’s erg average by a second or two, because eight rowers drive a hull that is nowhere near eight times heavier. Anyone quoting one universal erg-to-water correction has not accounted for boat class.

Calorie Estimate

Concept2’s own monitor uses a specific conversion, and it is not simply watts times four:

calories per hour = (watts × 4 × 0.8604) + 300

The factor of 4 assumes the body converts chemical energy to work at about 25% efficiency, the 0.8604 turns watts into kilocalories per hour, and the flat 300 is your resting metabolism, which keeps running while you row. A 2:00 split works out at about 997 calories per hour. Drop the +300 and you land on 808 instead, understating the total by nearly a fifth, which is why the PM5 figure never matches a back-of-envelope estimate.

Training Zones (Approximate)

Under 150W: easy and recovery. 150-200W: aerobic base. 200-250W: steady state. 250-300W: threshold. Above 300W: high-intensity intervals.

Treat those as a rough map, not a prescription. Absolute watt bands suit a 90 kg club man reasonably well and mislead almost everyone else, because 200 watts is genuinely easy for a large rower and close to threshold for a small one. Zones anchored to a percentage of your own 2K power travel far better between bodies.