Horsepower to Watts

What One Horsepower Looks Like on a Power Meter

Cyclists, rowers and their coaches live in watts. Crank-based meters, smart trainers and ergometers all report the same thing: the mechanical power a body is putting into the pedals or the handle right now. Sooner or later somebody asks how that compares with an engine, and the answer needs the horsepower figure turned into the athlete's own unit before it means anything.

Conversion factor: 1 hp = 745.6998716 W, the mechanical horsepower James Watt defined as 550 foot-pounds per second. So half a horsepower is 372.85 W — roughly the hour-long output of a professional road racer, and a number a strong amateur can hold for a few minutes at best.

Why the Comparison Is Fair

The horse set the bar at 746 watts

Watt picked a figure a working pit pony could sustain turning a mill wheel, so a horsepower was never a peak — it was a shift-long work rate, which is exactly the wrong comparison for a five-second sprint.

Pedals and oars measure alike

A crank meter and a Concept2 flywheel both report mechanical output at the point where the body meets the machine, so cycling and rowing numbers sit on one scale.

Duration decides the number

There is no single figure for a person. The same rider might show 1,200 W for five seconds, 400 W for five minutes and 250 W for an hour, spanning more than a factor of four.

Output, not energy burned

These watts are mechanical work delivered to the machine. The metabolic cost of producing them is four to five times larger, and belongs on a calorie scale rather than a horsepower one.

Turning an Engine Figure Into Numbers From Your Training File

The usual starting point is an argument in a clubhouse or a coach explaining an interval set: someone quotes a horsepower figure and everyone else needs it in watts to react to it.

Type the horsepower figure, fractions included

Enter 1, or 0.5, or 0.25 in the left field and watts appear as you type. Fractional values are the interesting ones here — a comma decimal separator works just as well as a dot, so 0,75 is accepted.

Attach a duration before you judge it

745.7 W means nothing on its own. Decide whether you are talking about a standing start, a one-minute effort or a threshold test, then compare against the matching column of your own power profile.

Reverse it when the meter speaks first

More often you have the watts already. Press the swap button (↔) to run W → hp and see what last night's session was worth: a 300 W steady state is 0.402 hp.

Divide by body mass for the useful ratio

Once the figure is in watts, dividing by kilograms gives the number that actually predicts climbing and boat speed. Copy the bare value — no unit, no spaces — straight into your training log or spreadsheet.

Meters do not all agree: pedal, crank and hub power meters read at different points in the drivetrain and typically differ by a couple of per cent, while an air-braked ergometer computes power from flywheel deceleration rather than measuring it directly.

Human Mechanical Output, From Commute to Track Sprint

Representative sustained and peak outputs across cycling and rowing, in the watts a meter would display and the fraction of a mechanical horsepower they represent.

Effort	Duration	Output (W)	Output (hp)
Track sprinter, standing peak	About 5 seconds	2 000 W	2.682 hp
Strong club rider, sprint peak	About 5 seconds	1 000 W	1.341 hp
Elite rider, all-out minute	1 minute	700 W	0.939 hp
Heavyweight rower, 2 km piece	About 6 minutes	496 W	0.665 hp
Professional road racer, threshold	1 hour	400 W	0.536 hp
Recreational rower, 2 km piece	About 8 minutes	203 W	0.272 hp
Keen amateur, threshold	1 hour	220 W	0.295 hp
Commuter, easy cruising	Indefinite	100 W	0.134 hp

Read down the hour column and the picture is humbling: even a professional at threshold is barely over half a horsepower, and an ordinary rider on the way to work makes about an eighth of one. Only in the top rows, over seconds rather than minutes, does a person go past 1 hp at all — which is why the pit pony, working steadily all day, was never an easy standard to beat.

Working With Power Numbers Off the Machine

Type an engine figure, read training watts

Both fields update live, so you can walk a whole power profile — five seconds, one minute, twenty minutes — without resetting between entries.

Swap when the ergometer got there first

The reverse direction turns a session average into a fraction of a horsepower, which is the version people actually want at the end of a hard piece.

Small fractions shown to eight decimals

Human efforts land well under 1 hp, so the extra decimals matter; large values are grouped with a space and switch to scientific notation only at extremes no athlete will reach.

Metric horsepower on the dropdown too

Searchable unit lists on both sides cover every power unit, so a figure quoted in PS by a European source drops in without a second tool.

Questions Riders and Rowers Ask About Horsepower

What fraction of a horsepower can a fit person hold for an hour?

A keen amateur cyclist sitting at 220 W for an hour is producing 0.295 hp. A professional at 400 W reaches 0.536 hp. Even the very best hour records, in the region of 440 W, come to about 0.59 hp — so no human has ever held a full horsepower for anything like an hour.

Can a person produce a full horsepower at all?

Briefly, yes. It takes 745.7 W, and a strong club rider hitting 1,000 W out of the saddle is already at 1.341 hp. Track sprinters peak past 2,000 W, or 2.682 hp. The catch is duration: those figures survive about five seconds, whereas the horse standard assumed the same output all day.

Why does a five-second number look impressive and an hour number look tiny?

Because two different energy systems are being drained. Short efforts run on stored phosphates and glycolysis, which deliver enormous power and empty in seconds. Anything beyond a few minutes has to be paid for aerobically, at a rate the heart, lungs and mitochondria can actually sustain — and that ceiling is far lower. Plot output against duration and the curve falls steeply for the first minute, then flattens.

Does watts per kilogram change how the horsepower figure reads?

It changes what the figure is good for. A 90 kg rower at 450 W is making 0.603 hp against a 60 kg climber's 300 W, or 0.402 hp — half as much again in absolute terms. Both are at 5 W/kg, so on a climb they would go up side by side, because gravity charges by mass. Convert to watts first and divide by body mass from there; horsepower per kilogram is not a ratio anyone uses.

Why do ergometers and power meters display watts rather than horsepower?

Resolution and habit. Training zones are set a few watts apart, and a scale where everything meaningful happens between 0.1 and 0.7 would be awkward to read on a console. Watts also drop straight into the physiology: the SI unit connects cleanly to joules of work and to W/kg, the ratio coaches actually prescribe against.