MPGe: A Misleading Metric for Comparing Gas vs Electric Cars?
We’re all looking for ways to save money, and when it comes to cars, fuel efficiency is a major factor. But comparing fuel economy between gasoline, hybrid, and electric vehicles can be tricky. While MPG (miles per gallon) is a straightforward metric for gasoline cars, MPGe (miles per gallon equivalent) for electric vehicles often leaves me confused.
Why MPGe Isn’t the Whole Story
MPGe is designed to offer a standardized way to compare gasoline and electric vehicles, but it fails to capture the true cost difference. The problem lies in the fact that MPGe is based on the energy equivalent of a gallon of gasoline. While it provides a rough comparison, it doesn’t account for differences in the prices of gasoline vs electricity, which vary significantly across the country.
The Importance of $/Mile
A more accurate way to compare fuel costs is to calculate the cost per mile driven. This calculation takes into account the local price of gasoline and electricity, providing a more realistic picture of fuel expenses.
Here’s how to calculate $/mile:
Gasoline Vehicles:
- Divide the cost of a gallon of gas by the vehicle’s MPG.
Electric Vehicles:
- Divide the cost of electricity per kilowatt-hour (kWh) by the vehicle’s MPGe, then multiply by 33.7.
Example:
Let’s compare a gasoline car with 30 MPG and an electric car with a 100 MPGe rating.
In this example, the electric car is about 2.5x cheaper to operate than the gas car rather than the 3.3x that you might want to believe when comparing 30 MPG and 100 MPGe.
Sensitivity Table: Fuel Cost Fluctuations
The cost difference between gas and electric vehicles can be drastically affected by changing fuel prices. The following table shows how $/mile varies with different gas and electricity prices:
What does this table mean?
If you live in a state where electricity and gas are both relatively expensive, like $0.20 and $4, then fuel costs about 2x more for this gas car vs this electric car (assuming 30 MPG and 100 MPGe). If you compare those 2 exact same cars in a place like Canada where gas is even more expensive but electricity is cheap, like $0.05 and $6, then the fuel costs over 10x more for that same gas car vs the same electric car. The 100 MPGe metric vs 30 MPG is quite misleading if you don’t take your local fuel costs into account.
While MPGe provides a useful point of comparison between electric vehicles, it doesn’t tell the whole story today since we’re comparing gas and electric. $/mile is more helpful (and more work to get).
