How Many Watts Does a Microwave Use? Monthly kWh and Compared With an Oven

How many watts does a microwave use?

• 800 W, averaging 640 Wh per hour of use, according to the table from Argentina’s electricity regulator (ENRE). It doesn’t draw the full 800 W the whole time.
• 750 to 1,100 W, according to the U.S. Department of Energy table reproduced by Virginia Tech.
• The guide from the EWEB utility lists 625 W for a 625 W microwave and 1,000 W for a 1,000 W one.

The figure for yours is on its rating plate. Use the watts listed there, which are what it draws from the outlet.

How much does it use per month?

With the ENRE figure, 640 Wh per hour of use:

• One 5-minute use: 640 × 5 ÷ 60 = 53 Wh.
• 15 minutes a day for a month: 640 × 0.25 × 30 = 4,800 Wh, about 4.8 kWh.

That’s what the electricity usage calculator gives for a microwave at a quarter of an hour a day. To put it in perspective, it’s less than one ceiling fan uses in a month at 8 hours a day (14.4 kWh, from the same table).

Microwave, oven or toaster: which uses less?

In the same ENRE table, a 25–30 litre (roughly 1 cu ft) electric oven is rated at 1,500 W and uses 750 Wh per hour; a 73 litre built-in oven, 2,450 W and 1,225 Wh; a toaster, 950 W. Hour for hour they’re similar, but a microwave heats a plate in minutes while an oven needs much longer.

Worked example: reheating dinner

1. In the microwave, 5 minutes: 640 × 5 ÷ 60 = 53 Wh.
2. In a 25–30 litre electric oven, half an hour (including warm-up): 750 × 0.5 = 375 Wh.
3. The oven uses 375 ÷ 53 = about 7 times more.
4. Doing it every day for a month: 1.6 kWh with the microwave versus 11.3 kWh with the oven.

The minutes are an example: change them to yours in the calculator. For a roast the oven is still the right tool; for reheating, the microwave uses far less.

If you run it on a generator or inverter

An 800 W microwave draws 800 W while it runs: if the fridge starts at the same time, add the fridge’s 200 W plus its start-up kick of about 600 W. We do that math in what size generator you need. On a battery, a microwave uses little per day because it runs for a few minutes, but the inverter has to supply its full wattage.

Common mistakes

• Thinking the microwave is one of the biggest users. It has a lot of watts but runs for minutes: per month it uses far less than the fridge (about 65 kWh, also from the ENRE table).
• Reheating small portions in the oven. For reheating, an oven can use several times more.
• Plugging it into a power strip with the kettle or toaster. Together they can exceed what the strip handles: check with the power strip calculator.

When to call an electrician or a technician

If the breaker trips when you start the microwave, the plug gets hot or there’s a burning smell, unplug it and call an electrician. If it sparks inside with no metal in it or doesn’t heat, don’t open it yourself: take it to a technician.