Horsepower Formula

Horsepower is an imperial unit of power of an engine. It is defined as the work done per unit time. The term Horsepower was invented by James Watt. It is a unit power that compares the power of a machine to the horse muscle power. Earlier it was used to measure steam engine power output compared to the power of draft horses. Later it was expanded to different types of piston engines, electric motors, turbines and other machinery.

One Horsepower equals to 33,000 lb. ft/min.

Horsepower formula is given as

Horsepower (HP) = (Torque × Speed)/5252

There is another Horsepower formula related to the weight given as

\(\begin{array}{l}\text{Horse Power , HP} = Weight \times \left ( \frac{velocity}{234} \right )^{2}\end{array} \)

This formula is applied to calculate the speed or velocity at the end of the run. Weight includes the mass of the whole body.

Example 1

Determine the horsepower of a car which moves with a speed of 600 revolutions per minute and has a torque of 100 pound-foot.


Given parameters are
Torque = 100 pound-foot
Speed = 600 revolutions per minute>

Horsepower formula is given by

Horsepower = (Torque × Speed) / 5252

HP = (100 × 600) / 5252

HP = 60000/5252

HP = 1.142 hp

Example 2
Calculate the speed of the vehicle if its horsepower is 0.865 hp and torque is 250 pound-foot.

Given parameters are

Torque = 250 pound-foot

Horsepower (HP) = 0.865 hp

The speed is given as

Speed = (Horsepower × 5252)/ Torque

Speed = (0.865 × 5252)/ 250

Speed = 4542.98/250

Speed = 18.17 revolutions per min


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