MPGe: miles per gallon equivalent explained and measured

Article by Christian A., on August 15, 2018

When buying cars, especially new ones, customers look for a couple of numbers. These numbers include but are not limited to the engine output and torque, top speed and fuel economy ratings. Yes, fuel economy ratings are important figures in car ownership. After all, you want to know how far your car can go before having to refill your fuel tank.

Fuel economy ratings are measured differently in different places. In the United States, fuel economy is measured by miles per gallon (mpg) while in other places like Europe, it is gauged by liters per 100 kilometers (l/100 km). Simply put, mpg means the number of miles your car can travel on a gallon of gasoline or diesel. On the other hand, l/100 km means the amount of fuel – as measured in liters – your car would consume in every 100 km travelled. For this article, we will focus on mpg.

Nonetheless, the actual mpg figure of your car might be different from its published rating from the US Environmental Protection Agency (EPA). This because the estimated mpg rating is measured by having a run on a dynamometer through two standardized driving schedules. In real world driving, your car may consume more or less fuel because of the varying traffic and weather conditions as well as on differences on how the car is driven.

However, there is a steady rise in the number of electrically powered vehicles in the market, including pure electric vehicles (EV) and hybrid vehicles. EVs don’t use conventional fuel, which means the mpg measurement isn't applicable to them. Hybrids, meanwhile, employ a combination of electric motors and conventional engines, which also makes the usual mpg gauge not applicable to them. To solve this dilemma, EPA came up with a more appropriate measurement for EVs and hybrids – MPGe, which stands for miles per gallon equivalent.

Essentially, MPGe is how EPA converts the power used by an EV or hybrid into mpg, a term that is most familiar to Americans. Unlike European drivers who are more concerned with the amount of fuel consumed per 100 km, Americans aren’t. Instead, Americans are more concerned with how many miles they could get on a certain amount of fuel. Of course, measuring the economy rating of EVs as miles per 100 kilowatt-hours is admissible. But Americans would rather want economy rating to be measured in mpg – thus the MPGe.

Simply put, MPGe is the number of miles your can travel using electricity (EVs) or electricity and gasoline (hybrids) with the equivalent energy content of one gallon of gasoline. The EPA employs an established energy standard of 115,000 BTUs (British thermal units) per gallon of gasoline. This means that when a gallon of unleaded gasoline is burned, it generates an amount of heat measured at 115,000 BTUs. To generate the same amount of heat, you have to consume 33.7 kWh of electricity.

If a car can travel 100 miles on 33.7 kWh of electricity, then its rating is 100 MPGe. A car that can travel 100 miles on 32 kWh of electricity consumes less electricity on such distance and is given a rating of 105 MPGe.

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