Mileage Calculator Methodology

Calculator Methodology and Environmental Impact

The core data for the Gas Mileage Impact Calculator comes from the ACEEE’s Green Book®: The Environmental Guide to Cars and Trucks. To produce the Green Book, ACEEE applies the highest degree of research and scrutiny to conduct a cradle-to-grave lifecycle analysis of the environmental impact of vehicles. Each vehicle is given an overall “green score,” as well as scores for environmental damage, health costs, and greenhouse-gas emissions.

You can learn more about their methodology, and even purchase their 70-page methodology report, by visiting the the Green Book methodology web page.

To produce the gas usage, cost, and carbon dioxide results for the Gas Mileage Impact Calculator, we use combined EPA highway and city mileage figures, averaged with a 55% to 45% weighting preference given to city driving. When you input the number of miles you drive and the cost per gallon, this allows us to calculate usage and cost. Once we know how many gallons of gas you are using in a certain period, we simply multiply that number by 19 to produce the pounds of carbon dioxide emitted—because every gallon of gas burned produces that amount of CO2 in the atmosphere.

EPA Numbers versus Real-Life Numbers

We realize that EPA fuel economy figures don’t always reflect real-world driving. To get a better sense of how your driving (e.g. speeding, jack-rabbit starts, etc.) may reduce the actual figures, click “evaluate driving style” at the bottom of the calculator results page. determined a percentage value for each driving trait based on careful research. The values are noted in parentheses on the driving style panel. These figures were not verified by ACEEE, and are intended to give you a general sense—not a precise, indisputable number—of how your vehicle’s fuel economy and environmental impact is affected by the way you drive. The driving style panel is irrelevant if you are tracking your mileage/impact on a tank-by-tank basis, which is a more precise way to derive actual numbers. This functionality can be launched from the bottom of the results table.

Adjusting driving traits will affect the calculator’s estimates of fuel economy and CO2 emissions. While these driving traits also affect the level of criteria pollutant emissions, these emissions are not easily quantified and are thus not shown in the calculator.

Pollutants and Emissions Levels

We relied entirely on ACEEE for their data regarding how much of the so-called "criteria pollutants"—emissions other than carbon dioxide—are being produced for each vehicle, and for each engine/emission level for the relevant vehicle. Please consult with ACEEE’s Green Book® methodology documentation to get a better understanding of how ACEEE quantifies emissions for these pollutants. The Calculator indicates pollution emitted while the vehicle is being driven, and does not reflect the total lifecycle of emissions.

Because so few people know the emissions level of their vehicle, we’ve offered the option of “not sure” in that dropdown. We generally select the most polluting of the “tiered” standards, or if the car is not rated in that way, the most polluting of the California standards. The selected standard, intended to give a mid-range emissions level, appears in the column header of the calculator’s results page. You can read more about these terms on our emissions standards page.


If you have any questions about the calculator, the methodology, or, please send us your feedback.