Diesel vs Gasoline Converter

Understanding Fuel Energy Equivalents

Diesel and gasoline contain different amounts of energy per gallon. A gallon of diesel fuel contains approximately 13% more energy than a gallon of gasoline, which is why diesel engines tend to get better fuel economy on a per-gallon basis. Fuel equivalents allow fair comparisons between different fuel types by normalizing them to the same energy content.

Energy Content of Common Fuels:

Key Conversion Formulas:

Diesel Gallon Equivalent (DGE): The amount of an alternative fuel that has the same energy content as one gallon of diesel.

DGE = fuel volume × (fuel BTU per gallon / 129,500)

Gasoline Gallon Equivalent (GGE): The amount of an alternative fuel that has the same energy content as one gallon of gasoline.

GGE = fuel volume × (fuel BTU per gallon / 114,000)

Diesel to Gasoline Conversion:

1 gallon diesel = 1.136 gallons gasoline (energy equivalent) 1 gallon gasoline = 0.880 gallons diesel (energy equivalent)

Watch the direction here, because it trips almost everybody. Those two lines are about volume: how much of one fuel holds the same energy as a gallon of the other. Fuel economy converts the other way round, and using the volume factor on an MPG figure is the single most common mistake in this subject.

MPG in fuel B = MPG in fuel A × (BTU per gallon of B / BTU per gallon of A)

So a vehicle doing 30 MPG on gasoline, burning energy at the same rate, would do 30 × (129,500 / 114,000) = 34.1 miles on a gallon of diesel. It goes further, not less far, because the gallon holds more energy. Multiplying by 0.880 instead gives 26.4 MPG, which is the answer to a different question entirely.

Separately, diesel engines are typically 20 to 35 percent more thermally efficient than gasoline engines. That efficiency gain stacks on top of the energy-density gain, which is why a real diesel car often beats the 34.1 figure rather than merely matching it.

Cost per BTU Comparison:

To fairly compare fuel costs: Cost per 100,000 BTU = (price per gallon / BTU per gallon) × 100,000

Practical Examples:

• Diesel costs $3.50/gallon and gasoline costs $3.00/gallon. Per 100,000 BTU: diesel = $2.70, gasoline = $2.63. In this scenario, gasoline is slightly cheaper per unit of energy.
• A diesel truck gets 25 MPG. Its gasoline-gallon-equivalent economy is 25 × (114,000 / 129,500) = 22.0 MPGe, so on energy alone it compares with a gasoline vehicle rated at 22 MPG, not 28. The 25 looks better than it is because a diesel gallon is a bigger gallon, energetically speaking.
• Converting a fleet from gasoline to diesel: if vehicles currently use 1,000 gallons of gasoline per month, they would need approximately 880 gallons of diesel per month for the same energy. This one is a volume conversion, so here the 0.880 factor is the right one.

Tips:

• MPG comparisons between diesel and gasoline vehicles are misleading without accounting for the different energy densities.
• The EPA uses GGE (gasoline gallon equivalent) for electric vehicles: 1 GGE = 33.7 kWh of electricity.
• Diesel fuel is denser than gasoline (about 7.1 lb/gallon vs 6.1 lb/gallon), contributing to its higher energy content per volume.
• Fuel prices vary by region and season. Always compare cost per BTU rather than cost per gallon for true economic comparison.