How to calculate microwave wattage

Written by alexis lawrence
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How to calculate microwave wattage
(Ryan McVay/Photodisc/Getty Images)

The wattage of your microwave determines how much electricity is required to run it and, therefore, how much it adds onto your monthly electric cost. Often the wattage of a microwave is listed either somewhere on the unit itself, generally on the back, or on the packaging that the microwave came in. If the wattage of your microwave is not listed on the unit or the packaging, it is possible to figure out the microwave’s wattage using other electrical measurements.

Skill level:

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Things you need

  • Ammeter

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  1. 1

    Determine the voltage of the microwave. The majority of microwaves in the United States run on the same voltage, 120 volts. It is possible, though, that your microwave runs on 110 volts. The voltage should be listed on the back of the unit somewhere near the plug. If it is not listed, use 120 volts for your measurement.

  2. 2

    Check the microwave to see if the amps are listed anywhere on the unit. If the amps are not listed on the unit, get an ammeter. This electrician's tool can be purchased online or at home improvement stores, such as Lowe’s or Home Depot.

  3. 3

    Clamp the ammeter around one of the wires coming from the back of the microwave. Turn the microwave on for approximately five seconds, or until the ammeter measures the current and displays a number. This number is the amperage, or amps, for your microwave.

  4. 4

    Multiply the amperage measured by the ammeter by the voltage of the microwave unit. The product is the number of watts that are used by your microwave. For example, a 2 amp microwave powered by the standard 120 volts would have a wattage of 240.

Tips and warnings

  • While a higher wattage microwave obviously uses more electricity while it is running than a lower wattage microwave, the former also cook more quickly than the latter, keeping energy consumption roughly even for both low and high wattage ovens.
  • According to Discovery’s Planet Green, microwaves are an energy-efficient alternative to cooking with a traditional oven.

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