How to Calculate Power Output

Physical power is defined as the amount of work done per unit time, where work is defined as the magnitude of force times the magnitude of displacement time the cosine of the angle between the directions of the force and the displacement. Physical power is measured in watts in the SI system and horsepower using English units. Electrical power is measure almost exclusively in watts and is defined as the voltage of a circuit time the amperage of the circuit.

Things You'll Need

• Work, force and displacement measurement sensors (for physical direct measurement methods)
• Multimeter (for electrical direct measurement methods)

Instructions

Physical Power

1. Obtain the work output. This can be done by direct measurement or by calculation. For the work calculation, you must obtain the force (f) and displacement (d) vectors, calculate the angle (a) between them and use the following equation:
   W = f*d*cos(a)

2. Obtain the amount of time it takes to perform the work calculated. This must usually be done by direct measurement unless it is provided through some outside source.

3. Divide the calculated work by the recorded time to obtain the value for power.

Electrical Power

1. Determine the voltage of the circuit you are analyzing. Many times you can use the output of the power source, but you can obtain a direct measurement using a multimeter.

2. Determine the amperage in the circuit. There are many ways to calculate this value depending on the make-up of the circuit, but the most direct method is to take a measurement with a multimeter.

3. Multiply the voltage by the amperage to obtain the value for electrical power output.