What size generator do I need for my house?
Check off everything you want to keep running during an outage. The calculator adds up running watts, handles the starting surge from your biggest motor, adjusts for altitude, and recommends a whole house generator size with a 20% safety margin. No email required.
The right whole house generator size depends on your appliances, not square footage: most gas-heated 2,000 sq ft homes land between 7,500 and 10,000 watts. Get your whole house generator size below.
Cooling & Heating
Kitchen
Water & Pumps
Laundry
Electronics & Lighting
Your elevation
Generators lose roughly 3% of their output for every 1,000 ft above sea level. If you live in Denver or the mountains, this matters.
Whole house generator size: why starting watts matter more
Anything with a motor (fridge compressor, AC, well pump) needs two to three times its running power for the second it starts. A generator that handles your running load but not the surge will trip its breaker every time the fridge kicks on. That is why our result is driven by starting watts, not just the sum of your appliances.
Whole house generator size: the 20% margin is not optional
Generators running at 100% load are loud, hot, and burn fuel fast. Keeping 20% headroom keeps the unit quieter and leaves room for the things you forgot to check off, like a phone charger or a garage door opener. If our recommendation lands between two sizes, round up.
Watts data source
Appliance wattage ranges come from Champion Power Equipment's published generator wattage chart. Your actual appliances may draw less; check the nameplate sticker on each unit if you want a precise number. When in doubt, sizing up is cheaper than sizing down.
Common questions
How big of a generator do I need for my house?
Check off your appliances above and the calculator answers it with your actual loads. As a starting point: gas-heated homes under 1,500 sq ft usually need 7,500-10,000 watts, and homes with central AC or all-electric heat need 16-22kW.
Will a 7,500-watt generator run a house?
It runs most of a small gas-heated home: fridge, freezer, furnace fan, lights, TV, internet, and either a window AC or a sump pump. It will not run central AC plus an electric water heater plus an electric dryer at the same time. Use the calculator with your actual appliances to be sure.
How big of a generator do I need for a 2,000 sq ft house?
Square footage alone does not decide it; your appliances do. Most 2,000 sq ft homes with gas heat land between 7,500 and 10,000 watts. All-electric homes of the same size often need 20,000 watts or more because of the electric water heater, dryer, and range.
Do I need a transfer switch?
Yes, for any generator wired into your home's circuits. A transfer switch keeps generator power from flowing back onto the grid, which is both a code requirement and a lineworker safety issue. Portable generators can instead power individual appliances through extension cords, but that means no furnace or well pump.