How the carbon calculator works

Our carbon calculator estimates the amount of carbon dioxide your car puts in the air every year, based on your mileage and the type of vehicle your drive. Several assumptions underlie this calculation, so the final number is meant to be an estimate only.

We start by assuming the gas mileage of your car based on the year, make, and model. Our data is derived from the Environmental Protection Agency's ratings, which you can explore more fully on their web site at fueleconomy.gov.

Next, we make an assumption about how much driving you do on highways vs. city streets. Most cars get better mileage on highways, because less braking means less wasted energy. For our calculations, we assume that you spend half your time on highways.

We then plug in the number of miles you drive each year. The average American drives 12,000 miles per year, but you can adjust this figure yourself. Using all of these numbers, we can figure out how many gallons of gas you burn every year.

Finally, we multiply the number of gallons of gas by 19.564 (for regular gasoline – diesel engines use a different factor) to figure out how many pounds of carbon dioxide your car puts out. The resulting number might seem high – a typical car puts out many times its own weight in carbon dioxide every year. But remember that when fuel burns, it combines with oxygen in the air and becomes much heavier.

Our estimate may differ slightly from the estimates you find on other web sites. One reason for the discrepancy may be that some web sites include other greenhouse gases that your car creates in addition to carbon dioxide. Other reasons could be that we use slightly different assumptions about your driving habits, or slightly different fuel ratings for your car.

Regardless of the source, you should find general agreement about the climate impact of your driving. And more importantly, now you can do something about it!

Can't find your car?

If your car is missing from our database, you can still estimate its yearly carbon output by telling us your car's average miles per gallon and the distance you drive each year:

Why is your car missing?

We derive our fuel mileage data from the Environmental Protection Agency's ratings. We've augmented the data with a few outside sources, but in general, if the EPA doesn't cover it, we don't either.

The EPA's data is mostly complete, but some gaps do exist. For example, some heavy trucks aren't classified as consumer vehicles, and therefore aren't included in the EPA's ratings.

If you can't find your car, you can try looking up a vehicle with a comparable year, weight, and body type. The results should be fairly accurate. And feel free to email us about the omission at info@terrapass.com. If we can find the data from an external source, we may add it at a later date.