What this calculator does
The rowing ergometer relates pace to power by a cube law: watts equal 2.80 divided by the cube of the pace, where pace is the 500 metre split in seconds divided by 500. A 2:00 split is 203 W and a 1:35 split is 408 W.
The cube is what makes erg improvement so unforgiving. Going from a 2:00 split to a 1:35 is 25 seconds, about 21% faster, and it requires almost exactly double the power. Every further second gets harder than the last, which is why split times compress so tightly at the top of any results sheet.
The formula
The split time in seconds is divided by 500 to give a pace in seconds per metre. Power is 2.80 divided by the cube of that pace. The constant and the cube relationship are what the Concept2 monitor itself uses, so the figure matches what the machine displays for a given split.
| Term | Meaning |
|---|---|
| Split | Time to cover 500 metres at the current rate, the standard erg pace unit. |
| Cube law | Power varies with the cube of speed, because drag on the flywheel rises with the square of speed and power is force times speed. |
| Drag factor | How much resistance the flywheel provides, which changes the feel but not the pace-to-watts relationship. |
| 2.80 | The Concept2 constant linking pace to power. |
The inputs explained
| Field | What to enter |
|---|---|
| 500 m split time (seconds) | The 500 metre split time in seconds. A 2:00 split is 120 seconds. |
When to use it
Converting between pace and watts
Training programmes are written in one or the other, and the monitor can display either, so the conversion comes up constantly.
Understanding why improvement slows
The cube law means each second off a split costs more power than the last, which explains a plateau that would otherwise look like stalled progress.
Comparing erg work against cycling
Watts are watts, so an erg figure can be compared directly against cycling power, though the muscles recruited differ considerably.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
What power does each split produce?
A range of 500 metre split times converted to power.
| Split time | Power output | Split time | Split in seconds |
|---|---|---|---|
| 1:35 | 408 W | 1:35 /500m | 95.0 s |
| 1:45 | 302 W | 1:45 /500m | 105.0 s |
| 2:00 | 203 W | 2:00 /500m | 120.0 s |
| 2:20 | 128 W | 2:20 /500m | 140.0 s |
Questions
Why is the relationship a cube?
Because drag on the flywheel rises with the square of its speed, and power is force multiplied by speed. Squaring and then multiplying by speed again gives a cube. The same relationship governs cycling against air resistance and boat hulls through water.
Does the drag factor change the watts?
No. The drag factor changes how the stroke feels and how the load is distributed, but the monitor calculates power from the flywheel deceleration and reports the same watts for the same pace regardless. Drag factor affects the stroke, not the arithmetic.
What is a good erg split?
For a 2,000 metre piece, under 2:00 per 500 m is a solid recreational benchmark for a man and under 2:15 for a woman. Competitive rowers go well under 1:40. Body weight matters considerably, since the erg does not carry the rower and heavier athletes have a real advantage.
How does erg pace compare to on-water speed?
Poorly, as a direct conversion. The erg measures power output with no hull, no water conditions and no technique penalty for a poor catch. Erg scores correlate with rowing ability but a fast erg does not guarantee a fast boat.
For cycling power relative to weight, see the power to weight calculator. For swim pace, see the swim pace calculator.