Microwave Wattage Explained: 700W vs 1000W vs 1200W
The wattage listed on the front of your microwave isn't the whole story. Learn the difference between cooking output watts and the electrical input watts your wall outlet sees.
The Two Numbers You Need to Know
When you buy a microwave, the box will proudly display a number like "1000 Watts." However, there is a fundamental misunderstanding about what this number means. It refers to the Cooking Output Power—the amount of microwave energy delivered into your food. It does NOT represent the total electricity the machine pulls from the wall.
To produce 1,000 watts of cooking power, the microwave's internal components (the magnetron, transformer, lights, and turntable motor) require significantly more energy. This total electrical draw is known as the Input Wattage.
Output Watts vs Input Watts
Microwaves are relatively inefficient at converting AC electrical power into microwave radiation. The magnetron inside the unit typically operates at about 60% to 70% efficiency. Because of this, the input wattage is always higher than the advertised output wattage.
| Advertised Cooking Power (Output) | Typical Electrical Draw (Input Watts) | Recommended Circuit Size |
|---|---|---|
| 600W - 700W (Compact / Dorm) | 900W - 1,100W | 15 Amp |
| 800W - 900W | 1,200W - 1,400W | 15 Amp |
| 1,000W (Standard Standard) | 1,500W - 1,600W | 15 or 20 Amp |
| 1,100W - 1,200W (Large / Over-Range) | 1,700W - 1,800W | 20 Amp Dedicated |
How Do Microwave Power Levels Work?
When you set your microwave to "50% Power" to defrost a steak, you might assume the microwave simply cuts the wattage in half and runs at 500W constantly. For most microwaves, this is false.
Traditional microwaves use a simple on/off transformer. They cannot modulate their power output. When you set it to 50% power, the magnetron turns on at 100% full blast for a few seconds, then shuts off completely for a few seconds. If you listen closely, you can hear a loud "clunk" or hum turning on and off during the cycle. The average power delivered over time equals 50%, but when it is actively humming, it is drawing the full electrical load from the wall.
Note: "Inverter Microwaves" (popularized by Panasonic) are the exception. They use an electronic inverter that can actually deliver a continuous, steady stream of lower wattage, providing a much smoother cooking cycle without the pulsing.
Why Recipe Times Rely on Wattage
Frozen dinners and microwave recipes usually provide instructions based on a baseline of a 1,000-watt to 1,100-watt microwave. If you own a small 700-watt compact microwave, you must extend the cooking time to ensure the food reaches a safe internal temperature.
Conversely, if you have a massive 1,200-watt over-the-range model, following a standard recipe might result in burnt edges or exploding soup. You should adjust the power level down to 80% to mimic a 1,000-watt unit.
How Much Does It Cost to Run a Microwave?
Despite their high input wattage, microwaves are one of the cheapest appliances to operate in your home. Why? Because they run for very short periods. Heating a bowl of oatmeal takes 2 minutes; you aren't running it for 8 hours a day like an air conditioner.
Cost Calculation:
- Electrical Draw: 1,500 Watts (Input)
- Daily Usage: 15 minutes a day (0.25 hours)
- Daily Energy: 1,500W × 0.25h = 375 Watt-hours (0.375 kWh)
- Annual Energy: 0.375 kWh × 365 = 137 kWh per year
- Annual Cost: 137 kWh × $0.15/kWh = $20.55 per year