Pick the appliances you want to keep running during a power outage. The calculator adds up running watts, accounts for the biggest motor start-up surge, adds headroom, and tells you which size class of generator to shop for.
Tick what you want to run at the same time during an outage. Numbers are typical estimates; your appliance's label or manual has the real figure.
Pick a few appliances to see a recommendation.
Safety: run any generator outdoors, at least 20 feet from doors and windows, with a CO alarm inside. Never back-feed a house through an outlet; use a transfer switch or interlock installed by an electrician.
How the numbers work
Running watts are what an appliance draws once it’s going. Starting watts are the short surge a motor (fridge, pump, AC compressor) needs to start. Motors rarely start at the exact same moment, so the calculator adds only the single largest surge on top of your running total, then rounds up with about 20% headroom so the generator isn’t running flat out.
- Under about 3,500 watts: an inverter generator or large portable power station usually covers it.
- About 4,000–9,000 watts: a mid-size portable generator, ideally dual-fuel.
- 9,000 watts and up: a large portable or a home standby generator.
Running a well pump? See generators for well pumps, since pump start-up surges are large. For the full walkthrough, read how many watts you need to run your house.