What is horsepower? How do I calculate my horsepower? These are common questions we receive from our customers. To answer this question, let’s first define what horsepower is.
Horsepower, like any unit of power, is simply a rate at which work is being done. Literally, the horsepower unit originates from an experiment which set out to measure the power of a single horse. It was determined that a horse is capable of performing 33,000 ft-lbf of work per min. We will address to this number later in the explanation.
First, a few equations to help you calculate your horsepower:
Power = Work / Time
Power = (Force x Distance) / Time
For electric motors, power or horsepower can be calculated from the torque and speed. For example, if you have a motor rated for 3,000 RPM and 6 in-lbf then the horsepower is calculated below.
Horsepower = (3,000 x 6) / 63,025 = 0.286
63,025 is a constant when using RPM for speed and in-lbf for torque units. 5,252 is another common constant if the speed is in RPM and torque is in ft-lbf. If the units are different then simply make the unit conversion.
The derivation of these constants is done using the 33,000 ft-lbf /min = 1 horsepower. Though horsepower units are a derivative of the 33,000 ft-lbf/min, it is not critical to understanding how to calculate motor horsepower for speed and torque.
Another common unit of power that motors are rated in is watts. The conversion from watts to horsepower is 745.7 watts = 1 hp.
To assist designers with sometimes difficult unit conversions Groschopp has developed The MOTORTEC STP calculator, a free, downloadable program that provides a fast, easy way to calculate speed, torque, or power. Conversions of the most commonly used units are selectable, automatically generated and can be printed out.
- Calculate Speed, Torque and Power
- Calculate Estimated Electrical Current and Losses for Optimum Motor Selection
- Easily and Accurately Convert Units of Measurement
- Customizable, Printed Report Function
- Calculate Operating Costs
