Combined MPG Explained: The EPA’s 55% City / 45% Highway Weighting
- Use Combined MPG to compare vehicles quickly.
- Check City MPG and Highway MPG for your commute.
- If your driving mix is different, estimate your own “blended MPG” using a simple miles-and-gallons method.
When you’re shopping for a car, the most prominent MPG number on the window sticker is usually Combined MPG. It’s popular because it’s one number you can use to compare vehicles quickly.
But it’s also one of the most misunderstood numbers. If your commute is mostly highway—or mostly short city trips—the combined value may not match what you actually see. The fix is simple: understand how combined MPG is defined, then personalize it for your driving.
What “Combined MPG” Means
Combined MPG is intended to represent a standardized blend of city and highway driving. EPA’s label documentation explains the three fuel economy values shown for gasoline vehicles: City MPG, Highway MPG, and Combined MPG. The combined value is featured for quick comparison across vehicles.
If you want a full breakdown of the label, start here: Understanding the EPA fuel economy label.
The 55/45 Weighting (EPA)
EPA’s gasoline label text states that combined fuel economy is calculated by weighting the City value by 55% and the Highway value by 45%. You can see this described directly in the Text Version of the Gasoline Label and in EPA’s interactive label materials.
How to Estimate Your Own Blended MPG
If you know a vehicle’s City MPG and Highway MPG, you can estimate a blended MPG that matches your driving mix by converting each part into gallons used, then recomputing MPG:
Example (math only): A car is rated 30 MPG city and 40 MPG highway. Your driving is 60 miles city + 40 miles highway.
- Gallons used = 60 ÷ 30 + 40 ÷ 40 = 2 + 1 = 3 gallons
- Blended MPG = 100 ÷ 3 = 33.3 MPG
Once you have a reasonable blended MPG estimate, you can quickly estimate cost with our Fuel Cost Calculator or compute fuel cost per mile with our Cost Per Mile Calculator.
When Combined MPG Can Mislead
Combined MPG is most useful when you use it for what it’s designed for: comparing vehicles under a consistent standard. It can be less representative if:
- You drive mostly highway or mostly city (the city/highway split is different).
- You take many short trips (engines spend more time cold and less efficient).
- You drive at higher speeds (fuel economy typically drops as speed rises).
- You use accessories heavily (air conditioning, defrosters, roof boxes, etc.).
EPA’s label fine print reminds shoppers that “your mileage will vary” due to driving, maintenance, weather, road conditions, and vehicle load (see EPA’s interactive label explanation of the fine print).
Estimate Your Real Fuel Budget
Use your own city/highway mix and gas price to estimate what you’ll actually spend.
Use the Fuel Cost CalculatorFrequently Asked Questions
Is Combined MPG the same as averaging City and Highway MPG?
Not necessarily. The label describes Combined MPG as a weighted result using a standardized city/highway split. For personal estimates, the most reliable approach is to compute gallons used for your expected city and highway miles, then divide total miles by gallons.
Why does EPA weight city miles more than highway miles?
EPA uses a standardized mix so shoppers can compare vehicles consistently. The gasoline label text states that City MPG is weighted at 55% and Highway MPG at 45% for the combined value.
Which MPG number should I use for my commute?
If your commute is mostly highway, start with Highway MPG. If it’s mostly stop-and-go, start with City MPG. If it’s a mix, Combined MPG is a good baseline—then personalize with your city/highway split and local conditions.
How do I convert these MPG numbers to L/100km?
For US MPG, a common shortcut is L/100km = 235.215 ÷ MPG. See our full guide: MPG to L/100km conversion.