Generator fuel use and runtime
The rating label does not tell you how much fuel a generator burns at your load. Enter the generator's gasoline rating, what you will actually run, and the fuel. We never fill in a fuel price: enter your own to get a cost per day.
How this is worked out
- Fuel energy: gasoline 33.7 kWh/gal (EIA), propane 27 kWh/gal, a 20 lb cylinder about 4.7 gal (DOE AFDC), natural gas about 10.36 therm per 1000 cf (EIA).
- Fuel use at your load is interpolated in a straight line between the 25%, 50% and 100% points. Below 25% we hold the 25% rate, which rounds fuel use up.
- Without chart points we use a generic estimate (25% of the full-load rate plus 75% scaled by load, about 20% fuel-to-electric efficiency). It is a typical value, not a measurement and not a test of any model.
- Dual-fuel generators make less power on other fuels: typically about 10% less on propane and 10 to 20% less on natural gas. We use 90% and 85%; change it to match your spec sheet. Fuel use per kWh delivered is assumed equal to gasoline.
- Propane cylinders: runtime assumes the whole 20 lb is usable, which is optimistic in cold weather; allow margin.
Compare ownership cost in generator vs power station vs home battery, or find your load with the backup power calculator.