Two numbers, and the label shows the wrong one
This is the single most useful thing on the page, and it catches almost everyone.
Cooking power is what the microwave delivers into the food. It is the number on the door, in the manual and in the listing — 700W, 900W, 1,000W, 1,200W.
Input power is what it draws from the outlet. A magnetron is roughly two-thirds efficient, and the turntable motor, fan, light and control board add a little more.
| Cooking power on the door | Typical draw at the wall | Inverter needed |
|---|
| 700 W | Around 1,000-1,100 W | 1,200 W or more |
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| 900 W | Around 1,300-1,400 W | 1,500 W or more |
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| 1,000 W | Around 1,400-1,600 W | 1,800 W or more |
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| 1,200 W | Around 1,700-1,900 W | 2,000 W or more |
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Input figures are typical ranges based on the roughly two-thirds efficiency of a magnetron plus accessories. Your own unit prints its input rating on a plate at the back or inside the door — reading a nameplate explains where to look.
So the rule of thumb is: add about 50% to the door number, then buy an inverter above that. A 1,000W microwave on a 1,200W inverter will not run, and that is exactly the disappointment this page exists to prevent.
The energy cost is trivial
Having established that the power draw is large, here is the other half: a microwave uses almost no energy, because it runs for minutes.
| Task | Run time | Energy at 1,500 W input |
|---|
| Reheat a mug of coffee | 1 minute | 25 Wh |
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| Reheat a plate of food | 3 minutes | 75 Wh |
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| Cook a frozen meal | 8 minutes | 200 Wh |
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| Boil two cups of water | 4 minutes | 100 Wh |
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Energy is input watts x minutes / 60. Times vary with the food and the unit.
A 1,056Wh battery therefore holds roughly a dozen plate reheats. The constraint is never capacity — it is whether the inverter can deliver 1,500W for those three minutes.
Standby draw, which is the annoying part
A microwave with a clock and a touch panel draws something in the region of 2 to 7 watts continuously, whether or not you use it.
Trivial on the grid. On a battery during an outage it is roughly 50 to 170 watt-hours a day — comparable to leaving a lightbulb on, for a clock you are not looking at.
The fix is to unplug it between uses when you are running on stored power. The same applies to the television, the cable box and anything else with a standby light.
Where it sits against the alternatives
Worth framing honestly, because a microwave is one of the better outage cooking options and one of the worst.
Better than it looks: it uses very little energy per meal, it heats food quickly, it produces no combustion products, and it works indoors — which none of the fuel-burning alternatives do.
Worse than it looks: it needs a large instantaneous draw, which is exactly what small batteries and small inverters cannot provide.
For a household with a 1,000Wh-plus battery, a microwave is a genuinely good outage cooking plan. The cooking without power page covers the propane alternatives for everyone else, and the camping watts page works the same arithmetic for a smaller setup.
The short version
- Add 50% to the door number. 1,000W cooking is about 1,500W at the wall.
- Size the inverter, not the battery. Energy per meal is tiny.
- 1,800W of inverter is the practical threshold for a standard household microwave.
- Unplug it between uses on battery — the clock costs more than the cooking.
