How to Test a Microwave

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Updated February 13, 2023

If you’ve just moved or are unboxing a new microwave, you need to make sure it’s in working order. You may think knowing how to test a microwave requires being an appliance repair technician, but that’s not the case. You can test your microwave oven power level at home with microwave-safe dishes. Even the best microwave oven can go bad over time, so read our guide below to check that your appliance is working correctly.


  • Take two microwave-safe containers made of glass and fill them each with two cups of room temperature water. Measure the starting temperature of each and average them together.
  • Place both containers in the microwave and cook them for one minute. Then, remove them and stir for a few seconds each.
  • Subtract the average starting temperature from the heated temperature and multiply by 70 to find the actual wattage output of your microwave.

How to Test a Microwave for Power Issues

Tools: Two glass containers, rubber gloves, thermometer, spoon

Over time, any kitchen appliance will start to act up. Whether you use a microwave pressure cooker or bake frequently in it, the device will eventually wear over time. The most common issue is a loss in microwave power due to a lousy microwave magnetron. The magnetron generates the output frequency required to heat frozen food or a cup of water. But, just like fixing a microwave handle, you can diagnose power issues on your own by following our guide.

Insider Tip

Only use microwave-safe pyrex or glass for your temperature tests. Using a plastic or paper dish will yield an inaccurate reading.

STEP 1 Fill Containers

Pour two cups of water into each glass container. Each glass of water should have an identical amount, and the water content should be room temperature.

STEP 2 Measure Starting Temperature

If you used cold water in the previous step, pour it out. You need room temperature water (about 68 degrees), or you’ll get an inaccurate reading. Use your thermometer to take the temperature of each container. Next, average these two numbers for our starting temperature.

STEP 3 Run the Microwave

Place each cup of water into the center of the microwave cavity. Set your cooking time on the default setting to one minute and let your microwave oven do the rest. The containers will be hot, so take each cup of water out one at a time. Consider wearing rubber gloves to protect your hands.

STEP 4 Measure the Heated Temperature

Quickly stir each cup of water to settle the heat. Next, use your thermometer to measure the water temperature in both glass containers. Average these measurements to get your heated temperature.

STEP 5 Find Your Microwave’s Wattage Output

Now that we have our two measurements, we can now find our microwave oven’s working wattage. Subtract the starting temperature (Step 2) from the heated temperature (Step 4) and multiply that figure by 70. You now have your microwave power in watts.

STEP 6 Compare Wattage with Advertised Power

Compare your results with the wattage advertised by your microwave manufacturer. If you’re just a few watts off, don’t worry. That said, if there is a wide margin, consider reaching out to the manufacturer or a local appliance store for help correcting the operating frequency. For more power issues, like a microwave door that trips your breaker, reach out to professionals.


Never test your microwave with stainless steel containers. They will spark and could cause an electrical fire.


Do all microwave ovens leak radiation?

Assuming your microwave is fully operational and undamaged, it will not leak a meaningful amount of electromagnetic radiation at all. In addition, microwave ovens are treated to prevent errant electromagnetic rays.

How to Test If a Bowl or Dish Is Microwave-Safe

Heat the dish in question alongside an established microwave-safe container filled with water for one minute. Then, remove both containers. If your new dish is hot, it is not microwave-safe. However, if the water is hot but your new dish is cool, you have a microwave-safe container.

How does a microwave cook food?

Microwave ovens use microwaves for cooking or grilling your food. The magnetron inside the appliance generates microwaves, and your food or beverage heats up as they absorb the energy.

STAT: A US Department of Energy survey found that the most common microwave cooking time is one to three minutes. (source)

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