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Tools  /  Generator Sizing   Free

What size generator, and how long will it run?

Check off what you need to keep running. This adds up the load the right way — steady watts plus the one big motor surge — tells you the smallest generator that will actually start it all, and how long a tank lasts. Undersize it and it stalls when the fridge kicks on; oversize it and you burn fuel you did not need to.

1

What you need to run

Add each load; edit its watts to match your gear.
2

Generator & fuel

Inverter units throttle the engine down and sip far less at light load.
gallons
Cycling a fridge only needs a few hours on.
3

Results

Generator to buy
Fuel & runtime

Notes

Only one motor surges at a time. The startup spike from a fridge or pump lasts a fraction of a second, so the generator only has to cover the largest single surge on top of everything already running — not every surge at once. That is the peak this sizes to, plus 20% headroom so the generator is not pinned at max. Never run a generator indoors or in a garage — carbon monoxide is invisible and kills; keep it outside, ≥20 ft from windows. Fuel figures are estimates for a loaded generator; inverter units sip less at light load, and propane gives somewhat less runtime per gallon than gasoline but stores indefinitely.