How Much Energy Is in a Gallon of Gasoline, Propane or Diesel?
By the Generator Size Calculator Team · Updated · 5 min read
Quick answer: The EIA lists gasoline at about 120,214 Btu per gallon, propane at 91,452 and diesel at 137,381. Dividing by the 3,412 Btu in a kilowatt-hour gives about 35.2 kWh of heat in a gallon of gasoline, 26.8 in propane and 40.3 in diesel. A generator turns only part of that into electricity. At an assumed 20% efficiency, a gallon of gasoline gives about 7 kWh.
The EIA numbers
| Fuel | Heat content per gallon |
|---|---|
| Motor gasoline | 120,214 Btu |
| Propane | 91,452 Btu |
| Diesel fuel | 137,381 Btu |
The EIA also says 1 kilowatt-hour equals 3,412 Btu, and notes that these factors are recalculated each year, so the figures may change a little.
From Btu to kilowatt-hours
| Fuel | Btu per gallon | Heat energy (kWh per gallon) | Compared with gasoline |
|---|---|---|---|
| Gasoline | 120,214 | 35.2 | 100% |
| Propane | 91,452 | 26.8 | 76% |
| Diesel | 137,381 | 40.3 | 114% |
Dividing by 3,412 gives the heat energy in kilowatt-hours. Propane carries about 76% of the energy of a gallon of gasoline, which is one reason a gallon of propane does not go as far. A pound of propane is a different measure from a gallon, so compare fuels by energy rather than by volume. See propane vs gasoline generators.
How much becomes electricity
A generator is a heat engine, and most of the fuel energy leaves as heat and exhaust. As an assumed example, if 20% of the energy becomes electricity, a gallon of gasoline gives about 7.0 kWh, propane about 5.4 kWh and diesel about 8.1 kWh. At that rate, a steady 1,000-watt load uses about 0.14 gallons of gasoline an hour. Real efficiency varies with the engine and the load, and engines are usually less efficient at light load, so your own fuel use figure is better than this estimate. The fuel consumption calculator works with real rates.
What to do with this
- Compare fuels by energy, not just price per gallon. See the running cost calculator.
- Use the maker's fuel consumption for your model and load. See the generator runtime calculator.
- Plan storage. See how long a generator runs on a tank of gas.
See how long your fuel will last.
Run the generator outdoors, at least 20 feet from the home. Never in a garage or shed. Carbon monoxide has no smell or color. See how far a generator should be from your house.
Frequently asked questions
How many kWh are in a gallon of gasoline?
About 35.2 kWh of heat energy by EIA figures (120,214 Btu divided by 3,412). A generator turns only part of that into electricity.
How many kWh are in a gallon of propane?
About 26.8 kWh of heat energy (91,452 Btu), around 76% of a gallon of gasoline.
How many kWh are in a gallon of diesel?
About 40.3 kWh of heat energy (137,381 Btu).
How much electricity does a generator make from a gallon of gas?
It depends on the engine and load. At an assumed 20% efficiency, about 7 kWh.
Is propane or gasoline better for a generator?
Gasoline carries more energy per gallon. Propane stores longer and burns cleaner. See the propane vs gasoline guide.
Related calculators
Sources: U.S. Energy Information Administration, British thermal units (Btu) (gasoline 120,214, propane 91,452 and diesel 137,381 Btu per gallon; 3,412 Btu per kilowatt-hour). The kilowatt-hour conversions are arithmetic. The 20% generator efficiency is an assumed example.