To determine the size of the generator needed, total the rated watts of the appliances and fixtures you'll want to operate during an outage. Some loads are easy to determine -- a 100-watt light bulb, for example, uses 100 watts. Then 10 bulbs would require 1000 watts, or 1 kW. The power requirements for appliances are often provided in the operating manual. These specifications are also stamped on the "face plate" along with the serial and model numbers.

While the power needs of individual appliances vary, those that produce heat or use large motors tend to require higher wattage.

An average 14 cubic-foot refrigerator with automatic defrosting, for example, requires about 615 watts while an electric range at 12,220 watts needs nearly 20 times as much power. Electric space heaters and water pumps are usually rated at 1000 to 1800 watts (1-1.8 kW) and electric water heaters require 2500 to 4400 watts (2.5-4.5 kW).

As you can see, a household's power requirements can quickly add up.

Wattage Reference Guide

Appliance or Tool
Running Wattage*
Startup Wattage*
3/8" hand drill
500
750
Jigsaw
600
900
Airless sprayer
700
1800
6" bench grinder
700
1800
Belt sander
1200
1700
Demolition hammer
1200
1800
7 1/4" circular saw
1500
1900
Portable heater
1500
1800
Furnace fan
1100
2000
Refrigerator/freezer
1200
3000
Sump pump
1700
3200
Clothes washer
1000
7500
Small refrigerator
500
2000
Light bulb
50
0
Home security
100
0
Television
400
0
Microwave
750
0
Toaster oven
1500
0
Air conditioner
(20,000 BTU)
3300
0
Water heater
4000
0
12v DC battery charger
200
0
Radio
225
0
Slow cooker
250
0
Electric blanket
1000
0
Electric skillet
1200
0
Coffeemaker
1200
0
* Wattage numbers are estimates. They will vary based on the wattage rating of the tool or appliance being used.