A portable generator for home emergency use is selected by how many total watts of power you will need for the electrical devices you want to operate. The basic formula is amps x volts = watts. For example, a 100 watt light bulb running on a 120 volts consumes one amp. If you wanted to run ten 100 watt light bulbs you would need: 10 x 120 = 1,200 watts.
