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Generator Sizing Calculator
Not sure what size generator you need? Tick the appliances you want to run during an outage and we'll calculate the wattage — startup surge included — and point you to the right generators.
Tick everything you want to run at the same time during an outage:
How generator sizing works
What size generator do I need to run my house?
Add up the running watts of everything you'll run at once, then add the single largest startup surge (only one motor starts at a time). Add ~20% headroom. Most homes need 5,000–7,500W for essentials, or a 12,000W+ standby generator to run the whole house including central AC.
What's the difference between running watts and starting watts?
Running (rated) watts is the continuous power a device uses. Starting (surge) watts is the brief spike when a motor kicks on — a fridge or AC can surge 2–3× its running watts for a second. Your generator must cover the peak surge, not just the running total.
Do I need a portable or a standby generator?
Portables (2,000–9,500W) are cheaper and cover essentials during outages. Standby generators (12kW–24kW) are permanently installed, start automatically on natural gas or propane, and power the whole home — the better choice for frequent outages or high loads.