Convert between mechanical, metric, and electrical horsepower, watts, and kilowatts. Calculate horsepower from torque and RPM.
| Unit | Value |
|---|---|
| HP – Mechanical | 100 |
| HP – Metric (PS) | 101.387 |
| HP – Electrical | 99.9598 |
| Kilowatts (kW) | 74.57 |
| Watts (W) | 74,569.99 |
| ft·lbf/s | 55,000 |
| BTU/hr | 254,443.24 |
| Type | Watts | Definition |
|---|---|---|
| Mechanical HP | 745.70 W | 550 ft·lbf/s |
| Metric HP (PS) | 735.50 W | 75 kgf·m/s |
| Electrical HP | 746 W | Exact by definition |
Mechanical horsepower and metric horsepower sound like one unit with two accents, but they are different sizes: 1 mechanical hp is 745.70 watts, 1 metric hp (PS) is 735.50 watts, and the gap is about 1.4%. A brochure that lists 200 PS describes an engine roughly 2.7 hp weaker than a spec sheet that lists 200 hp. This page converts between the horsepower variants, kilowatts, watts and ft·lbf/s, and has a second mode that turns torque and RPM into power.
Take an engine that makes 300 ft·lbf of torque at 3,000 rpm and ask what power that is.
Torque has to be in ft·lbf first. The page divides in·lbf by 12 and multiplies N·m by 0.737562 to get there. Here the torque is already in ft·lbf, so nothing changes.
Now the formula: HP = torque (ft·lbf) × RPM ÷ 5252. The constant comes from 33,000 ÷ 2π, which is 5252.11, and the page rounds it to 5252. So HP = 300 × 3,000 ÷ 5252 = 171.36 mechanical horsepower.
Everything else is a watt conversion. 171.36 hp × 745.69987 = 127,785.6 W, which the page shows as 127.786 kW. Divide the same watts by 735.49875 and you get 173.74 PS, the metric figure for that engine.
The Unit Converter tab works the same way in the other direction: your entry is multiplied into watts using the unit you picked, then divided by each target unit's watt size. 100 mechanical hp is 74.57 kW, 101.39 PS and 99.96 electrical hp. Horsepower values show up to four decimals, so a hand calculation may differ in the last digit.
Metric horsepower is defined as 75 kgf·m/s, which is 735.50 W. Mechanical horsepower is 550 ft·lbf/s, or 745.70 W. So 100 PS is only 98.63 mechanical hp. Check which one a spec sheet uses before comparing two engines.
Whichever the torque number describes. Feed it flywheel torque and you get flywheel horsepower; feed it torque measured at the rollers and you get wheel horsepower. The formula itself knows nothing about drivetrain loss.
Use the RPM at which that torque was measured. Torque and power peak at different speeds, so multiplying peak torque by redline RPM gives a power figure the engine never actually delivers.
Because HP = torque × RPM ÷ 5252. At exactly 5,252 rpm the division cancels and the two numbers are equal, provided torque is in ft·lbf. In N·m the crossing happens at a different place, or not on the same scale.
No. Here electrical horsepower is simply the unit, 746 W. A 5 hp motor delivers about 3,730 W at the shaft and draws more from the wall, because the page does not model motor efficiency.