Calculate the gasoline gallon equivalent (GGE) of CNG, propane, diesel, hydrogen, and electricity, convert GGE back to fuel units, and compare cost per GGE.
Gasoline Gallon Equivalent Formula
To convert an amount of an alternative fuel into its gasoline gallon equivalent, multiply the fuel amount by that fuel’s conversion factor:
GGE = A * CF
To find how much of a fuel you need to match a number of gasoline gallons, divide instead:
A = G / CF
To compare price, divide the fuel’s price per unit by the same conversion factor to get its cost for one gallon of gasoline worth of energy:
Cost per GGE = P / CF
Variables:
- GGE is the gasoline gallon equivalent, the number of gallons of gasoline that hold the same energy
- A is the amount of the alternative fuel, measured in its own unit (gallons, ccf, kWh, or kg)
- CF is the conversion factor for that fuel, in GGE per unit, taken from the table below
- G is the number of gasoline gallons you want to match
- P is the price of the alternative fuel per unit
The calculator runs in three modes. The first mode takes an amount of a fuel and returns its GGE plus the equivalent energy in BTU. The second mode reverses that math to tell you how many units of a fuel equal a set number of gasoline gallons. The third mode takes a price for the fuel and a price for gasoline and returns the cost per GGE for each, so you can see which fuel is cheaper for the same energy. One GGE is defined as about 114,000 BTU of lower heating value, which is also close to 33.7 kWh of electricity.
Fuel Conversion Factors and Cost per GGE
These are the Energy Policy Act (EPAct) conversion factors the calculator uses. The last column shows the reverse figure, how many units of each fuel it takes to equal a single gallon of gasoline.
| Fuel | Unit | GGE per unit (CF) | Units per GGE |
|---|---|---|---|
| Diesel | gallon | 1.14 | 0.88 |
| Biodiesel (B100) | gallon | 1.05 | 0.95 |
| E85 | gallon | 0.78 | 1.28 |
| Propane (LPG) | gallon | 0.74 | 1.35 |
| LNG | gallon | 0.66 | 1.52 |
| CNG at 2,400 psi | gallon | 0.18 | 5.56 |
| CNG at 3,000 psi | gallon | 0.22 | 4.55 |
| CNG at 3,600 psi | gallon | 0.26 | 3.85 |
| CNG | hundred cubic feet (ccf) | 0.81 | 1.23 |
| Electricity | kWh | 0.03 | 33.33 |
| Hydrogen (gas) | kg | 1.00 | 1.00 |
| Hydrogen (liquid) | gallon | 0.27 | 3.70 |
The factor only tells you about energy, not price. This next table shows how the same factors turn a per unit price into a cost per gallon of gasoline energy, using one set of sample prices. Plug your local prices into the cost mode to update these numbers.
| Fuel | Sample price | Cost per GGE |
|---|---|---|
| Gasoline | $3.39 / gallon | $3.39 |
| Diesel | $3.79 / gallon | $3.32 |
| E85 | $2.69 / gallon | $3.45 |
| Propane (LPG) | $2.79 / gallon | $3.77 |
| CNG | $1.10 / ccf | $1.36 |
| Electricity | $0.15 / kWh | $5.00 |
| Hydrogen (gas) | $14.00 / kg | $14.00 |
The cost column reorders the fuels in a way the sticker price hides. Propane looks cheaper than gasoline per gallon, but once you correct for its lower energy it costs more per GGE. Electricity at 15 cents per kWh looks tiny per unit, yet it takes about 33 kWh to equal a gallon of gasoline, so its cost per GGE lands well above the pump. CNG comes out cheapest here, which is why fleets track cost per GGE rather than price per unit.
Example Problems
Example 1: Convert a fuel amount to GGE.
You fill up with 8 gallons of propane and want the gasoline equivalent. Multiply the amount by the propane factor of 0.74:
GGE = 8 * 0.74 = 5.92 GGE, so that propane holds about the same energy as 5.92 gallons of gasoline.
Example 2: Compare cost per GGE.
Propane costs $2.79 per gallon and gasoline costs $3.39 per gallon. Divide the propane price by its factor:
Cost per GGE = 2.79 / 0.74 = $3.77. That is higher than the $3.39 gasoline price, so at these prices gasoline is the cheaper source of energy even though propane’s price per gallon looks lower.
Frequently Asked Questions
What is a gasoline gallon equivalent?
A gasoline gallon equivalent is the amount of an alternative fuel that holds the same energy as one gallon of gasoline, about 114,000 BTU of lower heating value. It lets you compare fuels that are sold in different units, such as kilograms of hydrogen, cubic feet of natural gas, or kilowatt hours of electricity, on one common scale.
Is GGE the same as a diesel gallon equivalent?
No. A diesel gallon equivalent (DGE) uses a gallon of diesel as the reference instead of gasoline. Diesel carries more energy per gallon, so one DGE is about 1.14 GGE. If a station lists a price per DGE, divide by 1.14 to put it on the same footing as a gasoline price.
Does a lower cost per GGE always mean lower fuel bills?
Not by itself. Cost per GGE compares the energy you buy, but not how efficiently your vehicle turns that energy into miles. An electric motor converts stored energy to motion far more efficiently than a gasoline engine, so a fuel can cost more per GGE and still cost less per mile. Use cost per GGE to compare the fuels, then adjust for your vehicle’s efficiency to compare the actual driving cost.
