Fuel Economy Ratings Explained

Fuel economy ratings are key when shopping for a car, but what do they really mean? This guide explains how they’re calculated, their real-world accuracy, and how to choose a car that fits your needs and budget.

Table of Contents

Why Fuel Economy Matters

Fuel efficiency isn’t just about saving a few dollars at the pump. It shapes your total cost of ownership and influences your environmental footprint. For many, good fuel economy is the difference between a manageable commute and a wallet-draining one. Efficient vehicles also release fewer emissions, reducing your impact on air quality and climate change.

What Do Fuel Economy Ratings Measure

Fuel economy ratings measure how efficiently a vehicle converts fuel into travel, usually expressed as miles per gallon (MPG) in the US. More miles per gallon means less fuel used to go a certain distance. For electric vehicles, the Environmental Protection Agency (EPA) uses an equivalent called MPGe (miles per gallon equivalent), which estimates how far the car can travel on the energy contained in one gallon of gasoline.

Most fuel economy labels list three figures:

City MPG

This measures efficiency in stop-and-go traffic, simulating city driving with frequent acceleration and braking.

Highway MPG

Designed to represent steady-speed driving on highways, involving less braking and fuel consumption.

Combined MPG

A weighted average (typically 55 percent city, 45 percent highway) that provides a general overview of efficiency across different driving conditions.

How Are Fuel Economy Ratings Calculated

The EPA oversees fuel economy testing in the United States. Automakers first conduct standardized lab tests, and the EPA audits a subset to ensure accuracy. Here’s how the process generally works:

Controlled Testing

Vehicles are put on dynamometers (think giant treadmills for cars) that simulate both city and highway driving cycles. These cycles include specific patterns of acceleration, deceleration, idling, and cruising speeds meant to mimic real-life usage.

Lab-to-Road Adjustments

Because driving in a lab may not reflect real conditions, the EPA adjusts results to account for factors like air conditioning use, cold starts, and faster speeds. These adjustments help bring ratings closer to what the average driver might experience.

Rating Publication

The final numbers are posted on window stickers, manufacturer websites, and official fuel economy databases.

The Limitations of Lab-Tested Ratings

Even with adjustments, EPA ratings are best viewed as guidelines rather than guarantees. Real-world fuel economy can differ for several reasons:

Driving Habits

Aggressive driving, frequent short trips, or heavy loads will burn more fuel than gentle acceleration and highway cruising.

Traffic Conditions

Stop-and-go rush hour traffic or hilly routes can reduce your efficiency compared to smooth highway drives.

Environmental Factors

Extreme heat or cold forces your car’s systems to work harder, and things like wind or rain can also impact fuel usage.

Vehicle Maintenance

Poor tire pressure, dirty air filters, or overdue engine tune-ups can cause your car to use more fuel than its rating suggests.

Interpretation Tips for Car Shoppers

Fuel economy ratings are an excellent starting point, but here’s how to make the most of them:

Compare Like With Like

Always compare ratings among similar vehicle types and sizes. A compact sedan is expected to have better fuel economy than a full-size SUV. Use ratings to pinpoint the most efficient in each class.

Beware of Manufacturer Claims

While automakers highlight the highest possible ratings, check the EPA label, consult independent reviews, and consider emissions tests like those in Provo for a balanced view.

Factor in Your Driving Style

If you primarily drive short distances in heavy traffic, focus on a model’s city MPG. Long highway commutes? Highway MPG will have a bigger impact.

Think Beyond Gas

If you’re considering a hybrid, plug-in hybrid, or EV, pay attention to MPGe ratings and look up estimated range under different conditions.

Use Fuel Economy Tools

Online resources, such as Fueleconomy.gov, provide real-world figures submitted by owners and can help validate or challenge official ratings.

A Word on Hybrids and Electric Cars

For hybrids, plug-in hybrids, and electric vehicles, fuel economy ratings look a bit different:

Hybrids show higher city MPG than highway, since electric motors are more efficient at lower speeds.
Plug-in Hybrids display electric-only range alongside combined MPG when operating in hybrid mode.
Fully Electric Vehicles highlight total range and MPGe instead of traditional MPG.

It’s important to remember that charging habits, outdoor temperatures, and driving style can lead to significant variations from the ratings.

Making an Intelligent Choice

While fuel economy is crucial, it’s only one factor in choosing your next vehicle. Balance it with reliability, safety, ongoing maintenance costs, and your unique needs. Still, by understanding these ratings and their context, you’re well-equipped to make a choice that’s kind to both your wallet and the planet.

Conclusion

Fuel economy ratings distill complex engineering and real-world variables into a single, easy-to-understand number. Treat these numbers as well-informed predictions, not certainties. Evaluate them alongside the realities of your daily drive, leverage independent resources, and don’t hesitate to ask dealers or manufacturers for clarification.