You will need a generator large enough to handle all of the equipment that you will operate at the same time. The kilowatt (kW) rating of a generator determines its output. You can choose between portable models for 3 to 15 kW or stationary models at 7 to 45 kW. The average home uses from 10 to 12 kW without an air conditioner.

Make a List

If the generator is to be used as a primary power source, you will need to inventory everything. If it is an emergency standby generator, only to be used in power outages, you need to decide what you want to protect. Clothes dryers, air conditioners, heaters and stoves use the most power, but may not be necessary during an outage. Make a list of everything that will likely run on your generator. Don't forget small appliances like light bulbs, hair dryers, TV, iron, toaster, and computer.

Include the Wattage

Every electric appliance has a tag showing how much power it uses. For light bulbs, just add up the wattage. Ten 100 watt bulbs is 1000 watts or 1kW. Usually the tag indicates watts or kilowatts, but some only show voltage and amperage. To determine wattage, simply multiply voltage times amperage. Add the wattage to everything on your list. Be sure not to confuse watts with kilowatts (kW).

Maximum Calculated Load

Calculate your maximum power by adding up the wattage of the most equipment you will likely use at the same time. But remember that a home generator works harder at full load. To be safe, select a size about 10% to 20% larger than your maximum calculated load. If you have any questions, consult an electrician.

Source:

Sizing Residential Generators

Sizing: Determine Your Power Needs