Fuel Economy vs Greenhouse Gas Ratings: How the EPA Label Connects Them
- MPG is about fuel use; GHG rating summarizes tailpipe CO2 on a 1–10 scale.
- Fuel economy improvements typically improve GHG rating for gasoline vehicles.
- You can estimate CO2 per mile from MPG using EPA’s published CO2-per-gallon figure.
The EPA fuel economy label is more than just MPG. It also includes an emissions snapshot—including a Greenhouse Gas rating and a Smog rating. These ratings help drivers compare vehicles beyond fuel cost alone.
If you want a full walk-through of the sticker layout, start here: Understanding the EPA fuel economy label.
What the GHG Rating Measures
EPA explains the Greenhouse Gas (GHG) rating on its Greenhouse Gas Rating page. The rating is displayed on the label as a 1–10 score, with higher ratings indicating lower tailpipe greenhouse gas emissions.
This rating is separate from MPG. MPG tells you about fuel use and cost; the GHG rating summarizes tailpipe CO2 emissions (which are strongly influenced by fuel consumed, but not identical to “total environmental impact”).
Why MPG and CO2 Are Linked (Gasoline Vehicles)
For gasoline vehicles, EPA’s label documentation explains that fuel economy and GHG emissions move together because CO2 is directly related to the amount of fuel consumed. That relationship is referenced in the gasoline label explanation (text version of the gasoline label).
In plain terms: if you burn fewer gallons to go the same distance, you generally emit less tailpipe CO2.
How to Estimate CO2 per Mile From MPG
EPA publishes a commonly used reference number: 8,887 grams of CO2 per gallon of gasoline. EPA includes this figure on its greenhouse gas rating explanation page. Using that, you can estimate tailpipe CO2 per mile:
Example (math only): If a vehicle gets 30 MPG, estimated tailpipe CO2 is 8,887 ÷ 30 ≈ 296 g/mile.
If you prefer a fuel-first comparison that’s directly tied to spending, EPA’s label also includes a fuel consumption rate in gallons per 100 miles. EPA notes in its interactive label that fuel consumption relates directly to fuel used and fuel expenditures. We explain that metric here: Gallons per 100 miles explained.
How to Use MPG + GHG Rating When Shopping
Here’s a practical approach:
- Use MPG and annual fuel cost to estimate budget impact (see: Estimated annual fuel cost on the EPA label).
- Use GHG rating as a quick emissions summary for tailpipe greenhouse gases.
- Use Smog rating to understand local air pollutant performance (see: Smog rating explained).
Estimate Your Fuel Cost per Mile
Use MPG and gas price to estimate fuel cost per mile and annual spending for your driving.
Use the Cost Per Mile CalculatorFrequently Asked Questions
Does higher MPG always mean a better GHG rating?
For gasoline vehicles, higher MPG generally means lower fuel burned per mile, which typically means lower tailpipe CO2. EPA describes the relationship between fuel economy and greenhouse gas emissions in its label documentation and GHG rating explanation.
Is the GHG rating the same as “total environmental impact”?
No. The label rating focuses on tailpipe emissions for the vehicle. It does not attempt to capture every upstream or lifecycle impact.
Where does the 8,887 grams CO2 per gallon number come from?
EPA publishes that reference figure as part of its fuel economy and greenhouse gas labeling explanation. See EPA’s Greenhouse Gas Rating page.
Is there a metric that relates more directly to fuel saved than MPG?
Yes. EPA includes gallons per 100 miles on gasoline labels and explains that fuel consumption relates directly to fuel used and expenditures. See: Gallons per 100 miles explained.