MPG Basics and Calculation Guides

Core formulas, conversions, and practical guidance for understanding fuel economy clearly.

Quick Summary This hub collects foundational MPG content: how to calculate fuel economy accurately, how to convert units, how to interpret city/highway ratings, and how to avoid common mistakes when comparing efficiency.

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If you are learning fuel economy fundamentals or want to sanity-check your current method, start with the guides below. They are organized to move from basic formulas to deeper interpretation and comparison topics.

Best Gas Mileage Cars 2026 The best gas mileage cars in 2026 are led by hybrids like the Toyota Prius (57 MPG combined) and Honda Civic Hybrid (49 MPG combined), which deliver dramatically better fuel economy than... CO2 Per Gallon of Gas: A Simple, Sourced Way to Estimate Emissions If you want to estimate tailpipe CO2 emissions from gasoline use, you need one reliable conversion factor and a clear boundary. EPA provides a commonly used factor: 8,887 grams of CO2... Combined MPG Explained: The EPA’s 55% City / 45% Highway Weighting The EPA’s Combined MPG is designed for quick comparisons, using a standardized mix of city and highway driving. EPA’s gasoline label documentation explains that combined fuel economy is... Flex Fuel Vehicles: How to Tell If You Can Use E85 E85 is a high-ethanol fuel that can only be used in flex-fuel vehicles (FFVs) . FuelEconomy.gov provides a practical checklist for identifying an FFV (labels, fuel door markings, and... Fuel Economy Myths: What’s Fact vs Fiction (DOE) There’s no shortage of “MPG hacks” online. DOE publishes a “Fuel Economy Fact and Fiction” guide that addresses common claims about fuel-saving techniques. The big theme: a few basics... Fuel Economy vs Greenhouse Gas Ratings: How the EPA Label Connects Them The EPA label includes both fuel economy (MPG) and a Greenhouse Gas (GHG) rating on a 1–10 scale. For gasoline vehicles, these are closely linked because tailpipe CO 2 emissions... Gallons per 100 Miles Explained (Fuel Consumption Rate) Gallons per 100 miles is a fuel consumption metric shown on the EPA label for gasoline vehicles. Unlike MPG, it maps directly to fuel used and therefore to fuel cost . Lower is better.... How to Download FuelEconomy.gov Data (CSV) for Research FuelEconomy.gov (DOE) provides downloadable fuel-economy datasets (CSV) covering vehicle MPG, MPGe, fuel type, and related fields. It's a strong source for building comparisons,... Short Trips vs Long Trips: Why Cold Starts Use More Fuel Short trips often have worse MPG because engines spend a bigger share of the drive warming up and running less efficiently. DOE’s fuel economy guidance notes that taking several short... Smog Rating on the Fuel Economy Label: What It Measures The EPA fuel economy label includes a Smog rating on a 1–10 scale. It summarizes tailpipe pollutants that contribute to local air pollution (often called “smog-forming emissions”).... Speed and Fuel Economy: What Happens Above 50 MPH Speed has a measurable effect on fuel economy. The U.S. Department of Energy notes that gas mileage typically decreases rapidly at speeds above 50 mph and that speeding can reduce fuel... The MPG Illusion: Why MPG Isn’t Linear (and What to Use Instead) MPG is a useful number, but it’s not linear. The same “+10 MPG improvement” can mean very different fuel savings depending on where you start. That’s why EPA includes a fuel consumption... Understanding the EPA Fuel Economy Label (City, Highway, Combined MPG) The EPA fuel economy label is a standardized window sticker for new vehicles that helps you compare fuel use, costs, and emissions across models. The most prominent number is Combined... Does Air Conditioning Use More Gas? Yes, does air conditioning use more gas is a question with a definitive answer—running your car's AC can reduce fuel economy by 5% to 25% depending on driving conditions, outside... Highway vs City MPG: Why They Differ and What It Means Highway MPG is typically 20–30% higher than city MPG for conventional gasoline vehicles because steady-speed cruising is far more fuel-efficient than the constant stopping and... How Do You Calculate Your Miles Per Gallon? To calculate your miles per gallon (MPG), divide the total miles you drove by the number of gallons of fuel used. Fill up your tank, reset your trip odometer, drive normally, then fill... How to Save Money on Gas Learning how to save money on gas can cut hundreds of dollars from your annual fuel budget through smarter driving habits, regular vehicle maintenance, and strategic fueling choices.... MPG to L/100km: How to Convert Fuel Economy Units To convert MPG to L/100km, divide 235.215 by your US MPG figure—for example, 30 MPG equals roughly 7.8 L/100km. If you are working with Imperial (UK) MPG, divide 282.481 instead,...

Want to apply these concepts immediately? Use the Gas Mileage Calculator and compare against our FAQ reference as you track your own data.