How to Test Your Microwave's Wattage
Fill a Microwave-safe container with 1 carefully measured liter of water, preferably at room temperature, about 70F, and measure its temperature (Fahrenheit) as accurately as possible. Write that temp. down, and place the container in the microwave. Set the timer for 2:03, and hit start. (If yours is a 'mechanical timer' type, with just a dial, use a stopwatch - this must be accurately timed.)
Carefully measure the ‘end’ temperature and multiply the difference by 19.4. The result is the approximate energy gain in watts. (I know you’re wondering about those 3 seconds - it takes about that long for the magnetron tube’s filament to heat and start to ‘fire’, and we want exactly 2 minutes of heating)
Keep in mind that it’s normal for a microwave to produce less energy as it ages, but your results should be within about 50-75 watts of the rating.
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