Calculating How Long a Tank or Stored Fuel Supply Will Last

Last updated July 2, 2026

Determining how long a given quantity of fuel will last requires combining the fuel quantity with your expected rate of consumption, expressed in gallons per day or gallons per week based on planned usage. For a vehicle with a 14-gallon tank averaging 28 MPG and 35 miles of daily driving, daily fuel consumption is 1.25 gallons, meaning a full tank lasts approximately 11 days under that usage pattern. This calculation becomes more critical in scenarios involving fuel scarcity, extended trips without reliable refueling access, or emergency preparedness planning where running out of fuel carries real consequences.

For generators and other stationary fuel-consuming equipment, the calculation shifts to hours of runtime rather than miles. A generator consuming 0.75 gallons per hour at a moderate load will run for approximately 13 hours on a 10-gallon fuel supply. Stored fuel also degrades over time. gasoline without stabilizer additives begins losing combustibility within three to six months, while properly stabilized fuel can remain usable for up to a year or more. Any fuel-last calculation for stored or emergency fuel should account for this degradation timeline, particularly for fuel held in reserve for infrequent use such as backup generators or seasonal equipment.

The calculation shows fuel duration by dividing your available fuel quantity by your actual consumption rate, whether expressed in gallons per mile or gallons per hour depending on the equipment involved. For stored fuel intended for emergency or infrequent use, factor in the degradation timeline and consider fuel stabilizer additives to extend usable storage life beyond the typical three to six month window.