When it comes to evaluating the efficiency of electric vehicles (EVs), the concept of MPGe (miles per gallon of gas equivalent) often comes to the forefront. This metric, introduced by the Environmental Protection Agency (EPA), aims to provide a standardized way to compare the energy efficiency of vehicles across different fuel types. However, as we'll delve into, the intricacies of MPGe ratings can be confusing, especially when comparing vehicles with disparate power sources. The story of MPGe began in 2010, when the EPA introduced the concept to help level the playing field for alternative-fuel vehicles. Initially, MPGe ratings were optional for the 2012 model year and became mandatory in 2013. As part of the update, Monroney labels (the revised window stickers) gained information about a vehicle's greenhouse gas and other emissions. This new information aimed to provide a more comprehensive understanding of a vehicle's environmental impact. So, how is MPGe ...
When it comes to evaluating the efficiency of electric vehicles (EVs), the concept of MPGe (miles per gallon of gas equivalent) often comes to the forefront. This metric, introduced by the Environmental Protection Agency (EPA), aims to provide a standardized way to compare the energy efficiency of vehicles across different fuel types. However, as we’ll delve into, the intricacies of MPGe ratings can be confusing, especially when comparing vehicles with disparate power sources.
The story of MPGe began in 2010, when the EPA introduced the concept to help level the playing field for alternative-fuel vehicles. Initially, MPGe ratings were optional for the 2012 model year and became mandatory in 2013. As part of the update, Monroney labels (the revised window stickers) gained information about a vehicle’s greenhouse gas and other emissions. This new information aimed to provide a more comprehensive understanding of a vehicle’s environmental impact.
So, how is MPGe calculated? Simply put, it presents energy use in one form (electricity, hydrogen, or natural gas) in terms of another (liquid gasoline). The U.S. government’s conversion for this equivalence states that the amount of energy in a gallon of gas is equal to 33.7 kWh. Vehicles with multiple power sources have ratings for each mode; a plug-in hybrid has its electric-only and combined efficiency expressed in MPGe, while its gas-only number is in plain mpg.
For example, the most efficient version of the 2025 Toyota Prius PHEV (the model formerly known as Prius Prime) has a combined efficiency rating of 127 MPGe when running on electricity stored in the battery, while on gas alone it’s rated at 52 mpg combined. We can double-check the EPA’s math using the 26-kWh-per-100-miles rating that’s also on the label—expressed as miles per kWh, that would be 3.85, and then converting from electricity to its gasoline equivalence yields 130 MPGe.
When is MPGe useful? In a nutshell, it helps level the playing field when comparing vehicles with different fuel sources. For instance, an EV with a 120-MPGe EPA combined rating is vastly more efficient than a gas-powered vehicle with a 40-mpg-combined rating. The Prius PHEV’s two combined numbers make the efficiency advantage of electric propulsion very plain.
However, there’s a catch. MPGe ratings can be misleading, especially when comparing vehicles with different power sources. Electricity, measured in kWh, goes into the battery and is then used to run one or more electric motors. There’s no good reason to think of that in terms of gasoline; since battery capacity and consumption are most commonly expressed in kWh, it’s more natural to look at the amount of electricity required for the vehicle to travel a certain distance—the EPA has chosen 100 miles.
In conclusion, MPGe ratings provide a useful metric for comparing the efficiency of vehicles across different fuel types. However, it’s essential to understand the intricacies of these ratings and how they’re calculated. By doing so, you’ll be better equipped to make informed decisions when choosing your next vehicle.
COMMENTS