TRS Question of the Month

Question of the Month: How can I compare the energy content of alternative fuels and gasoline or diesel? What implications does this have for overall fuel and vehicle comparisons?


Alternative fuels have varying energy densities and are measured using a number of different units, which can make comparing them tricky. The gasoline gallon equivalent (GGE) unit allows drivers to make apples-to-apples comparisons of a given quantity of energy from alternative fuels and assess which fuel best suits their needs. Understanding the energy content of fuels can help inform comparisons of fuel prices and vehicle driving range.

What is a GGE? How about a DGE?

A GGE is a standardized unit used to compare the energy content of all fuels. This unit quantifies the amount of alternative fuel that has the equivalent energy content of one gallon of conventional gasoline. For medium- and heavy-duty vehicle fuel applications, diesel gallon equivalent (DGE) is often used.

How are GGE and DGE values determined?

Energy content is measured in British thermal units (Btus) per gallon of fuel, and is often referred to as the lower heating value of the fuel. To calculate GGE and DGE, the energy content of one gallon of gasoline or diesel is divided by the energy content of the comparison fuel. For example, conventional gasoline has an energy content of 116,090 Btus per gallon, while propane has an energy content of 84,250 Btus per gallon. As such, 1.38 gallons of propane has the same amount of energy as one gallon of conventional gasoline.

The table below displays the energy content, GGE, and DGE values of conventional and alternative fuels.


Energy Content*

Quantity of Fuel in 1 GGE

Quantity of Fuel in 1 DGE


116,090 Btu/gallon

1.00 gallon

1.11 gallon

Low Sulfur Diesel



0.90 gallon

1.00 gallon

Biodiesel (B20)

126,700 Btu/gallon

0.92 gallon

1.01 gallon

Biodiesel (B100)



0.97 gallon

1.07 gallon

Compressed Natural Gas (CNG)

923 Btu/cubic foot (ft3) or

20,160 Btu/lb

125.77 ft3


5.76 lb

139.21 ft3


6.37 lb

Liquefied Natural Gas

21,240 Btu/lb

5.47 lb

6.05 lb

Ethanol (E100)

76,330 Btu/gallon

1.52 gallon

1.68 gallon

Ethanol (E85)**

88,258 Btu/gallon

1.32 gallon

1.46 gallon



Btu/kilowatt hour (kWh)

34.00 kWh

37.64 kWh


84,250 Btu/gallon

1.38 gallon

1.53 gallon


288.88 Btu/ft3


51,585 Btu/lb

401.86 ft3


2.25 lb

444.78 ft3


2.49 lb

*Lower heating value. Source for CNG and hydrogen (Btu/ft3): Transportation Energy Data Book, Edition 35. Source for remaining values: Alternative Fuels Data Center (AFDC) Fuel Properties.

** E85 that is sold in the United States today actually contains, on average, approximately 70% ethanol. Therefore, E85 energy content calculated as [(.70) x (E100 energy content)] + [(.30) x (gasoline energy content)]

*** Electric vehicles are more efficient (on a Btu basis) than combustion engines, which should be taken into account when calculating and comparing miles per GGE (see below).

The values in the table above can help standardize fuel amounts for comparisons. For example, if you have 10,000 ft3 of CNG, you can determine the equivalent number of GGEs by dividing by 125.77 ft3 to get 79.5 GGE. Similarly, to determine the number of DGEs, you would divide by 139.21 ft3 to get 71.83 DGE.

How are GGE and DGE used to compare fuel prices?

Fuel prices can be represented in dollars per GGE or DGE for consistency in pricing between fuels. For that reason, the Clean Cities Alternative Fuel Price Report shows prices on an energy-equivalent basis (Table 3 in recent reports, If values for price per GGE or DGE are not available, you can do the calculation on your own. For instance, if one gallon of E85 is $2.04, you would multiply by 1.32 (see table above) to find that this price equates to $2.69 per GGE after adjusting for energy content.

What are the factors that impact how far I can drive between fill ups?

The energy content of fuels is one factor that affects driving range. Filling up with a less energy-dense fuel often means that you will not be able to drive as far. However, tank size and vehicle efficiency also play a significant role.

Some alternative fuel vehicles (AFVs) have similar tank sizes to conventional vehicles, while others have larger fuel tanks to compensate for the difference in energy content. For example, vehicles that run on propane and biodiesel typically have similarly sized fuel tanks as their conventional fuel counterparts. As you can see in the table above, both of these fuels have lower energy densities than their conventional fuel counterparts, which subsequently can result in lower fuel economy and shorter range per tank. In the case of propane, bi-fuel vehicles are available that can operate on both conventional fuel and propane for extended driving range. In addition, propane and biodiesel offer many other benefits that can offset this difference.

CNG and hydrogen vehicles, on the other hand, often have larger tanks to offset the lower energy densities associated with these fuels. Fleets and drivers purchasing a CNG vehicle may have the option to install an additional CNG storage tank onboard the vehicle. Alternatively, bi-fuel CNG vehicles are also available to extend the range. As for hydrogen, these vehicles tend to have larger fuel tanks overall.

Tank size is not the only other factor that affects range; vehicle efficiency also plays a role. For instance, all-electric vehicles (EVs) are significantly more efficient than conventional gasoline vehicles. According to, EVs use anywhere from 59% to 62% of the electricity from the grid to power the vehicle, while conventional gasoline vehicles can only convert 17% to 21% of the energy from gasoline to power the vehicle ( This is one reason why EVs have such significant fuel economy advantages over conventional vehicles, even when you are comparing the fuels on an energy-equivalent basis.


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TRS Question of the Month

A photo of a white EV sedan plugged in to a charging station located inside of an employee parking garage.

Question: What factors do employers need to consider when establishing a workplace charging program?

Answer: While there is not a one-size-fits-all solution for workplace charging, there are a number of resources available to help employers design, implement, and manage the right program for their organization.

Assess Demand

Employers considering whether workplace charging is right for their organization will want to start by assessing employee demand with an employee survey ( Once this assessment is complete, employers may set goals for meeting workplace charging demand, either by planning to meet the entire need (i.e., all drivers that have expressed or will express interest in PEV charging) or by dedicating a percentage of parking spaces to PEV charging. For example, Google has a goal to dedicate 5% of all parking spaces to workplace charging.

Procure and Install

Employers should determine what types of charging stations to purchase. There are a few decisions to make, including the following:

  • Charging Level: There are benefits and drawbacks to both Level 1 and Level 2 charging stations in the workplace. Employers must evaluate which option is best for their facilities. For more information about the differences between charging levels and their merits for workplace charging, see the U.S. Department of Energy’s (DOE) Workplace Charging Station Basics page (
  • Networking: Charging station networks provide maintenance, customer service, and energy monitoring capabilities, and collect payment on behalf of the station owner. However, networks require a fee, and employers will need to consider whether the convenience of charging networks outweighs the financial cost. For more information, see the DOE’s Workplace Charging Level 2 page (

Employers should also be sure to get quotes from a number of charging station providers. For more guidance, see the DOE’s Workplace Charging Sample Request for Proposal document ( Employers will work with their electrical contractor to determine charging station placement; station installation can be an expensive process, but employers can minimize costs by siting stations in locations that require minimal trenching, boring, and electrical panel upgrades. For more information about siting and installation, see the DOE’s Workplace Charging Equipment and Installation Costs page (                                                              


A well-managed, well-planned workplace charging program can ensure station access to all employees, promote strong communication between employers and station users, and encourage responsible station use.

  • Registration and Liability: Many employers require employees to register their PEV, which allows the employer to identify the number of vehicles using their charging stations. For example, employers can give registered vehicles a mirror hangtag or window sticker that identifies the vehicle as having permission to use the charging stations. A registration form may also include language that requires vehicle owners to agree not to hold the employer responsible for any damage to the vehicle that occurs while it is parked at the charging station. For more information, see the DOE’s Workplace Charging Registration and Liability page (

  • Station Sharing: It is important to emphasize that workplace charging is a privilege, not a right. Employees may be obligated to share stations with their colleagues and comply with established charging time limits. While an employer can set up systems for sharing stations, such as reserving the station (similar to how an employee would reserve a conference room) or establishing a set schedule for use, most employers allow users to resolve station-sharing conflicts themselves. However, it is important to establish consequences for violating station policies, such as using a station for less than four hours. By framing workplace charging as a privilege, an employer reserves the right to restrict access for employees that routinely violate company policy. For more information about how to establish workplace charging policies and encourage station sharing, see the DOE’s Workplace Charging Station Sharing page (

  • Pricing: While most employers offer workplace charging for free, charging for station use can be a good way to manage demand. Employers may charge for electricity (e.g., per kilowatt hour) or for time (e.g., per hour), depending on preference and applicable regulations. Employers can motivate employees to move their vehicles and share the stations by charging a nominal fee (or no fee) for the first set number of hours (e.g., four hours) and then raise the fee for subsequent time that the vehicle is parked in the space. For more information, see the DOE’s Workplace Charging Pricing page (

For more resources about workplace charging, see the DOE’s Workplace Charging website (, explore the Clean Cities’ Workplace Charging Toolkit ( /), or contact the TRS at

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