Torque to hp Calculator

The Torque to hp Calculator connects the three numbers that describe a rotating machine: how hard it twists (torque), how fast it spins (speed), and how much work it can do per second (power). Enter any two — torque and speed, or torque and power, or speed and power — and the calculator fills in the rest, then shows the result in watts, kilowatts, or BTU/h and in whichever horsepower definition you select.

This is the everyday tool for reading an electric-motor nameplate, checking an engine dyno sheet, or comparing a motor against a pump or compressor that needs a certain power. It is especially useful because engines and motors are often quoted in torque at a given rpm, while the equipment they drive is quoted in power — the conversion between the two is exactly what this calculator automates.

1. 1Enter the two values you already know — for example Torque and Speed. You can start from any pair: torque + speed, torque + power, or speed + power.
2. 2Pick the units that match your data using the dropdowns. Torque accepts $\mathrm{N\cdot m}$ or $\mathrm{lbf\cdot ft}$; speed accepts rpm, rad/s, or Hz; power accepts milliwatts through gigawatts plus BTU/h.
3. 3Read Power and Horsepower. For horsepower, choose the definition that matches your equipment — hp(I) mechanical is the default and the most common.

The calculator works in SI units internally. Torque is stored in newton meters, speed in radians per second, and power in watts, where the relationship is a simple product:

with $T$ the torque in newton meters, $\omega$ the angular speed in radians per second, and $P$ the power in watts. Because most machines report speed in revolutions per minute, the calculator converts rpm to radians per second before multiplying:

Horsepower is then a unit conversion from watts using the definition you selected — mechanical hp(I) uses $745.6998715823\ \mathrm{W}$, metric hp(M) uses $735.49875\ \mathrm{W}$, electric hp(E) uses exactly $746\ \mathrm{W}$, and boiler hp(S) uses $9812.5\ \mathrm{W}$.

Torque is the twisting force a machine can deliver; it decides how easily something accelerates or pulls from a standstill. Power is how fast that work is done — it is what lets you sustain speed. A truck and a sports car can make similar horsepower while producing very different torque curves, which is why both numbers matter.

“Horsepower” is not one fixed unit. The calculator includes the five definitions you will most often meet:

When comparing quoted power, make sure both values use the same definition — an electric-motor spec in hp(E) and an engine spec in hp(I) differ by roughly 0.3%, which rarely matters, but boiler horsepower is a much larger unit and is easily mistaken.

If your torque is in inch-pounds or foot-pounds rather than newton meters, the inch-pounds to foot-pounds converter converts between those imperial torque units before you bring the value back here.