EV Emissions Tool FAQ

Published Sep 25, 2015 Updated Jul 11, 2022

Table of Contents

Why do you need my ZIP code?

The emissions from charging an EV depend on the mix of electricity sources used to power your electricity grid. Here, we average those emissions at a regional level and use your ZIP code to identify what region you’re in. The ZIP code is only used to determine emissions in your area: we don't store any information submitted through the form.

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What types of cars does this tool include?

Our database includes most plug-in hybrid electric and battery electric vehicles currently on the US market with EPA fuel efficiency ratings, plus several years of older models. The tool does not include hybrid cars that don’t plug-in (“conventional hybrids”). While the use of an electric motor in conventional hybrids generally increases their fuel efficiency, they are refueled solely by gasoline and aren’t considered electric cars.

Hydrogen fuel cell electric vehicles are also not included in the current version of the tool. Information about the emissions from fuel cell electric vehicles can be found here.

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What is CO2e?

Different energy sources produce different global warming emissions. Carbon dioxide (CO2) is the most prevalent of these emissions, but other air pollutants—such as methane—also produce global warming.  To make comparisons easier, we convert the global warming potential of all emissions to units of carbon dioxide equivalent, or CO2e—the amount of carbon dioxide required to produce an equivalent amount of warming. This lets us compare gasoline emissions with emissions from the electricity grid, even if the chemical nature of the air pollution is different.

A higher number of CO2e emissions leads to more warming.

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How do you calculate a gasoline vehicle’s CO2e emissions?

To calculate CO2e emissions from gasoline-powered cars, the CO2e of tailpipe emissions is added to emissions from producing and transporting gasoline. We use data from the GREET model (Argonne National Laboratory) to calculate the emissions from extracting crude oil, transport to a refinery, conversion to gasoline, delivery to a filling station, and burning in a car engine.

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How do you calculate an electric vehicle’s CO2e emissions?

To calculate an EV’s emissions, we first identify where the car is charged. This tool matches a ZIP code with an electric grid region, which in turn is matched with an average emissions number (expressed as CO2e). The average emissions are calculated using data from the Environmental Protection Agency’s eGrid for direct emissions and the GREET model (Argonne National Laboratory) for indirect emissions (such as mining and the delivery of fuels to powerplants).

We use vehicle efficiency data from the Environmental Protection Agency (fueleconomy.gov) to determine the plug-in vehicle's electricity and gasoline consumption (if applicable) on a per mile basis. If the vehicle is a plug-in hybrid, we use a factor (termed "utility factor") to estimate the proportion of miles that will be driven on gasoline. This factor depends on the vehicle’s all-electric range. Plug-in hybrids with a longer electric range have a higher fraction of miles assigned to electricity.

The actual emissions generated by charging an EV can also depend on factors not considered in this analysis, including but not limited to the electric utility you choose (we average emissions from all electric utilities in a given region), presence of home solar panels, voluntary purchase of lower-emission electricity, and individual driving behavior.

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Why is my EV dirtier or cleaner than regional or national EV averages?

The emissions generated by driving an EV depend on both the grid it’s charged from and the vehicle’s efficiency in using that energy to move. Since different vehicles have different efficiencies, they are responsible for different emissions over any given distance, even when they’re charged off the same grid. Specific electric vehicle models may result in more or less CO2e per mile than the average cars modeled here.

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What if I have solar panels at home or buy green power?

This tool calculates the average emissions from utility-scale electric generation at the regional electricity grid level. Drivers that have home solar panels will have lower or no emissions from driving an electric vehicle when calculated using the method used in this analysis (average emissions from generation). Consumers who purchase “green power” are also responsible for lower emissions than the regional average calculated in this tool.

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What is the miles per gallon equivalent?

Emissions from EVs can be described in terms of a “miles per gallon equivalent.” For a given EV and electricity region, this measures the fuel economy a gasoline-powered car would have to achieve to generate an equivalent amount of global-warming pollution.

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How do you calculate regional and national averages?

We use the average new gasoline car (31.7 mpg) as the baseline for gasoline-powered cars, and 23.8 mpg for the average SUV, at both the local and national levels. Our model accounts for global warming pollution generated both upstream—ie, during oil extraction, refining, and transportation—and downstream, when it’s combusted in the vehicle’s engine.

To determine a national average for charging emissions, we average the emissions of the grids where EVs are sold today, based on 2016-2021 registration data—a “sales-weighted” national emissions average.

We also use sales-weighted numbers to determine vehicle efficiencies based on 2016-2021 electric vehicle sales. For battery electrics, we find an average national sales-weighted efficiency of 0.297 kilowatt hours/mile. Plug-in hybrids have an average national sales-weighted electric efficiency of 0.381 kilowatt hours/mile, an average gasoline efficiency of 35.4 miles per gallon, and an average electric range of 28 miles.

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What about emissions from vehicle production and disposal?

This tool estimates carbon emissions from EV charging, but doesn’t include pollution from vehicle or battery manufacturing or disposal. Those emissions vary by vehicle, but tend to be higher for electric vehicles than gasoline-powered ones, as battery manufacturing is energy and resource intensive. Over the vehicle’s lifetime, however, the global warming emissions benefits of driving on electricity far outweigh the emissions costs of vehicle manufacturing; most EVs “pay back” their production emissions within one or two years of driving, a period that will shorten as electricity grids get cleaner.

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Read more about manufacturing emissions in our in-depth analysis of life cycle EV emissions, "Driving Cleaner" (2022).

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