Generator sizing calculator
Check the appliances you want to run during an outage and set quantities where you have more than one. Totals update as you go, and the recommended size accounts for motor surge plus headroom.
Loading appliance data…
Your totals
Select at least one appliance and we'll work out the size.
Generators that fit your load
Select appliances above and we’ll match real models to your load.
Matched on the fuel you pick, not the brochure number — most standby units put out less on natural gas than on propane. Top three cheapest matches are flagged as best matches; the full highlighted list lives in the model database.
How this calculator works
Every appliance has two numbers. Running watts are what it draws once it is going. Starting watts are the brief surge a motor pulls in the first seconds after switch-on — a well pump or air conditioner can pull two to three times its running load while starting.
Your generator has to survive both. We total the running watts of everything selected, then add the single largest surge increment — the biggest (starting − running) difference among your selected appliances — on the assumption that motors rarely all kick on in the same second. That sum is the starting load.
Finally we apply roughly 20% headroom so the generator is not running flat-out at its rating (which shortens engine life and leaves nothing for the load you forgot), and round up to the next standard home standby size: 7.5, 10, 14, 18, 22, 24, or 26 kW. Treat the result as the size class to shop in; the model database shows what that class actually costs and burns.
A load-management module or smart thermostat can stagger motor starts and sometimes let you drop a size class — worth asking your installer about before you buy up.
Typical appliance wattage
The same figures the calculator uses. Check the nameplate on your own equipment where you can — older appliances, especially fridges and pumps, often draw more than the typical values below.
| Appliance | Category | Running watts | Starting watts | Notes |
|---|---|---|---|---|
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Next steps: take your recommended size to the generator model database, then the cost guide and fuel & runtime guide.