A gasoline gallon equivalent, or GGE, is the amount of an alternative fuel that carries the same energy as one gallon of gasoline. The reference point is roughly 114,000 British Thermal Units (BTU), based on gasoline’s lower heating value.1Alternative Fuels Data Center. Fuel Properties Comparison Every alternative fuel — compressed natural gas, propane, hydrogen, electricity, ethanol, biodiesel — is converted into that same energy unit, so pounds, kilograms, gallons, and kilowatt-hours can be compared honestly against a familiar baseline.
What a Gasoline Gallon Equivalent Is
A BTU is the heat needed to raise one pound of water by one degree Fahrenheit. One gallon of conventional gasoline produces roughly 112,000 to 116,000 BTU depending on the blend, and the industry rounds to about 114,000 BTU as the working benchmark.1Alternative Fuels Data Center. Fuel Properties Comparison Every other fuel is measured by how much of it delivers that same energy.
The reason the unit exists is physical. Compressed natural gas sits under high pressure. Liquefied natural gas is cooled to roughly negative 260°F. Hydrogen is sold by the kilogram. Propane is a pressurized liquid. Electricity comes in kilowatt-hours. Without an energy yardstick, there is no honest way to compare what a driver or fleet is buying. The GGE strips away physical form and measures the work each fuel can perform.
Conversion Factors by Fuel
The National Institute of Standards and Technology publishes the standard conversions used across the fuel industry. NIST Handbook 130 sets one GGE of compressed natural gas at 5.660 pounds.2NIST (National Institute of Standards and Technology). Uniform Laws and Regulations in the Areas of Legal Metrology and Fuel Quality (NIST Handbook 130) The Department of Energy publishes conversion factors for the rest:3U.S. Department of Energy. Fuel Conversion Factors to Gasoline Gallon Equivalents
- Propane (LPG): 1 gallon equals 0.74 GGE, so about 1.35 gallons of propane match one gallon of gasoline. For tax purposes, one GGE of propane equals 5.75 pounds.
- Hydrogen: 1 kilogram equals 1 GGE.
- Electricity: 33.7 kilowatt-hours equal 1 GGE. This figure is the basis for the EPA’s MPGe rating on electric vehicle window stickers.
- Ethanol (E100): 1 gallon equals 0.67 GGE, reflecting ethanol’s lower energy density.
- Biodiesel (B100): 1 gallon equals 1.05 GGE.
Each factor comes from dividing the fuel’s lower heating value into the gasoline baseline. CNG and hydrogen use weight-based measures because their volume shifts sharply with temperature and pressure, so weighing the fuel gives a more reliable reading than measuring tank space.
When the Measure Switches to Diesel
Liquefied natural gas does not use GGE. Because LNG almost exclusively powers heavy-duty trucks that would otherwise burn diesel, it is measured against diesel’s energy content instead. One gallon of diesel contains about 128,488 BTU, roughly 13% more energy than a gallon of gasoline.4Alternative Fuels Data Center. Fuel Properties Comparison The resulting unit is the Diesel Gallon Equivalent (DGE), and NIST Handbook 130 sets one DGE of LNG at 6.059 pounds.2NIST (National Institute of Standards and Technology). Uniform Laws and Regulations in the Areas of Legal Metrology and Fuel Quality (NIST Handbook 130) If you see LNG priced or taxed by the “gallon equivalent,” it almost certainly means DGE, not GGE.
CNG can also be expressed in DGE when it replaces diesel in heavy-duty applications. NIST puts that figure at 6.384 pounds of CNG per DGE.2NIST (National Institute of Standards and Technology). Uniform Laws and Regulations in the Areas of Legal Metrology and Fuel Quality (NIST Handbook 130) For federal tax purposes, though, CNG is always taxed against the gasoline equivalent, regardless of the vehicle it powers.
Comparing Fuel Costs Using GGE
The everyday use of the GGE is price comparison. Divide the total cost of an alternative fuel purchase by the number of gasoline gallon equivalents delivered. Pay $12.00 for 8 GGE of CNG, and your effective cost is $1.50 per GGE, directly comparable to the per-gallon gasoline price at the pump next door.
For electricity, the EPA applies the 33.7 kWh conversion to produce a miles-per-gallon equivalent (MPGe) rating on window stickers.5U.S. Environmental Protection Agency. Fuel Economy and EV Range Testing An EV rated at 100 MPGe travels 100 miles on the energy equivalent of one gallon of gasoline. To translate a kWh rate into cost per GGE, divide your rate by 0.030, since 1 kWh equals 0.030 GGE.3U.S. Department of Energy. Fuel Conversion Factors to Gasoline Gallon Equivalents At a national average around $0.16 per kWh, that works out to roughly $5.33 per GGE. The higher figure looks bad on paper, but EV efficiency of 3 to 4 miles per kWh means the per-mile cost still undercuts gasoline in most markets.
For fleets running mixed vehicles, the GGE collapses pounds, kilograms, gallons, and kilowatt-hours into one number. A budget built around gasoline translates directly, and a manager can see at a glance whether a CNG truck or a diesel truck costs more to run per mile. The conversion covers the energy-cost piece only. Maintenance, infrastructure, and vehicle efficiency all sit outside it.
How GGE Sets Federal Excise Tax Rates
Internal Revenue Code Section 4041 taxes alternative motor fuels by energy equivalence rather than raw volume or weight. Different fuels are pegged to different baselines:6Office of the Law Revision Counsel. 26 USC 4041 – Imposition of Tax
- Compressed natural gas: 18.3 cents per energy equivalent of a gallon of gasoline, with one GGE defined as 5.66 pounds.
- Liquefied petroleum gas (propane): 18.3 cents per energy equivalent of a gallon of gasoline.
- Liquefied natural gas: 24.3 cents per energy equivalent of a gallon of diesel.
- Liquid fuels from coal or biomass: 24.3 cents per gallon.
The statutory 5.66-pound figure for CNG matches the NIST weights-and-measures standard, so the number on the dispenser is the same number the tax is calculated against.
What You See at the Pump
Retail CNG and LNG dispensers are required to label the equivalent they use. Under NIST Handbook 130, a CNG dispenser must display a permanent, conspicuous label stating: “1 Gasoline Gallon Equivalent (GGE) means 5.660 lb of Compressed Natural Gas,” or the corresponding DGE statement where CNG replaces diesel. An LNG dispenser must display: “1 Diesel Gallon Equivalent (DGE) means 6.059 lb of Liquefied Natural Gas.”2NIST (National Institute of Standards and Technology). Uniform Laws and Regulations in the Areas of Legal Metrology and Fuel Quality (NIST Handbook 130)
Separately, the Federal Trade Commission requires retailers selling any automotive fuel to post the fuel’s rating on every face of every dispenser, placed as close as practical to the displayed price per unit and kept legible. A dispenser selling two or more fuels with different ratings needs a separate label for each, and the retailer must hold a certification of the fuel rating from its supplier.7eCFR. 16 CFR 306.10 – Automotive Fuel Rating Posting Together the two rules mean the pump face should tell you what unit you are being sold, what mass or volume that unit represents, and what its rating is, before you agree to the price.