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How to Calculate Power & Current

Calculating power and current in a circuit follows Ohm's Laws, related to electricity. Power is usually measured in watts, such as the rating in light bulbs. Current is measured in amps. In most cases, you know know the voltage of a system, which is typically 120 volts in the U.S. for alternating current, i.e., household plugs. Batteries use a different voltage, but it is usually printed on the battery, so you know that as well. The other piece of information you need is the resistance in a circuit, which can be measured with a multimeter.

Instructions

  1. Calculating Current

    • 1

      Acquire the necessary data, which will be voltage and resistance. Both can be measured with a multimeter by choosing the appropriate option on the multimeter and testing the wires or resisters. These figures can usually be references as well in product specifications.

    • 2

      Calculate current, in amps, using the formula: Current equals voltage divided by resistance.

    • 3

      Plug in your data. As an example, suppose you calculated a 240 ohm resistance on a light bulb running of 120 volts, then:

      Current = Voltage / Resistance

      Current = 120 / 240

      Current = 0.5 amps

    Calculating Power

    • 4

      Acquire the required data, namely current and voltage. If you worked through the current calculation, you should already have both values.

    • 5

      Calculate power, in watts, using the formula: Power equals voltage multiplied by current.

    • 6

      Plug in your data to calculate the power of the lightbulb:

      Power = Voltage X Current

      Power = 120 X 0.50

      Power = 60 watts

Other Higher Education
Other Higher Education
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