Generator Sizing Calculator
Estimate generator watts for home backup power.
Use this generator sizing calculator to estimate the wattage required for home backup power. Add the continuous running loads and the starting surge of the largest motor, then choose the next standard generator size. A 5–7.5 kW generator typically covers essentials, while 12–20 kW can run most of a home, including central AC.
Peak load
7,500
watts
Continuous
5,000
watts
Buy at least
7.5 kW
common generator
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Recommended tools & materials
Handy picks for this project on Amazon.
Wire Stripper
Clean strips for 10–20 AWG
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Digital Multimeter
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Non-Contact Voltage Tester
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Wire Connector Assortment
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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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