Generator Sizing Calculator — Watts Needed

How the generator sizing calculator works

Total watts = sum of continuous running loads + starting surge of the largest motor. Then step up to the next standard generator size (kW).

5–7.5 kW covers essentials (fridge, lights, furnace fan). 12–20 kW runs most of a home including central AC.

Motors (AC, well pump, fridge) draw 2–3× their running watts for a moment when starting. Undersized generators stall.

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