Generator Sizing Calculator
Estimate generator watts for home backup power.
Generator size is the sum of running watts for everything you'll run at once, plus the largest single motor's starting surge (typically 2–3× its running watts). Essentials — fridge, furnace fan, sump pump, lights, Wi-Fi — usually land at 3,500–7,500 watts; whole-house standby runs 14,000–24,000. Enter your appliances for running and surge watts.
How does the generator sizing calculator work?
Total watts = sum of continuous running loads + starting surge of the largest motor. Then step up to the next standard generator size (kW).
What else do people ask about this calculator?
What size generator for a house?
5–7.5 kW covers essentials (fridge, lights, furnace fan). 12–20 kW runs most of a home including central AC.
Why add starting watts?
Motors (AC, well pump, fridge) draw 2–3× their running watts for a moment when starting. Undersized generators stall.
Which related calculators should I use next?
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