Runtime & Fuel Cost Calculator
Estimate hours per tank, gallons per hour and what a three-day outage costs on gasoline, propane, diesel or natural gas.
That works out to about 4.2 kWh per gallon, and you would need roughly 30.2 gallons on hand for the whole outage.
Your generator
A 20 lb barbecue cylinder holds about 4.7 gallons of propane; a 100 lb cylinder about 23.6; a residential tank is usually 250 or 500 gallons and is filled to 80 percent.
How this is calculated
Small air-cooled engines burn a meaningful amount of fuel even at light load, so consumption is modelled as a fixed share of the rating plus a load-proportional share, roughly gal/hr = kW × (0.06 + 0.12 × load) on gasoline. Other fuels are converted by energy content: 120,000 BTU per gallon of gasoline, 91,500 for propane, 138,000 for diesel and 1,030 per cubic foot of natural gas, with a 28 percent efficiency credit for diesel engines.
Estimates only. Your manufacturer publishes consumption at 25, 50 and 100 percent load, and those figures beat any model. Inverter generators do better than this at light load; older open-frame units often do worse.