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. Ten 100 bulbs would require 1,000 watts, or 1 kilowatt (KW). The power requirements for appliances are often provided in the operating manual. These specifications are also stamped on the “face plate” along with serial and model numbers.