Car CO2 Emissions per Mile and per Trip

The starting number: CO2 per gallon

The EPA publishes one figure for each common fuel. Burning a gallon of gasoline produces about 8,887 grams of CO2. Burning a gallon of diesel produces about 10,180 grams. In pounds that is about 19.6 and 22.4.

That looks impossible at first, because a gallon of gasoline weighs only about 6.3 pounds. fueleconomy.gov explains the gap: most of the weight of the CO2 comes from oxygen in the air, not from the fuel. When gasoline burns, its hydrogen joins oxygen to form water and its carbon joins oxygen to form CO2. A carbon atom weighs 12 and each oxygen atom 16, so every 12 units of carbon become 44 units of CO2. Gasoline is about 87% carbon by weight, which is about 5.5 pounds of carbon per gallon, and 5.5 × 44/12 comes to roughly 20 pounds of CO2.

The metric figure follows from the EPA number and the size of a US gallon, 3.785412 liters: 8,887 ÷ 3.785412 is about 2,348 grams of CO2 per liter of gasoline.

Two details matter less than people expect. Most gasoline in the US is blended with up to 10% ethanol. The EPA says fuel economy is slightly lower with the blend, but tailpipe CO2 per mile stays similar, because ethanol has less carbon per gallon than gasoline. And cars emit small amounts of other greenhouse gases: methane and nitrous oxide from the tailpipe, and hydrofluorocarbons from leaking air conditioners. The EPA says these are small compared with CO2, although they have a higher warming effect per gram. This guide counts CO2 only, as the EPA's per-gallon figures do.

Grams per mile by fuel economy

Because the CO2 per gallon is fixed, the only thing that changes from car to car is how many gallons it needs per mile. Here is the table for gasoline across common fuel economy figures, with diesel at the same mpg for comparison. The L/100 km column helps if your car reports liters per 100 km.

The 22.2 mpg row is the EPA's own example. The agency assumes the average gasoline vehicle on the road gets about 22.2 mpg, and states that the average passenger vehicle emits about 400 grams of CO2 per mile. The table gives 400 grams for that row, so the arithmetic matches.

Notice how the gains shrink as mpg rises. Going from 15 to 20 mpg saves 148 grams a mile. Going from 40 to 50 mpg saves only 44. Fuel use, and therefore CO2, follows gallons per mile, not miles per gallon. The MPG calculator page explains why L/100 km behaves in a straight line and mpg does not.

The diesel column holds mpg constant to show the fuel difference alone. A gallon of diesel emits about 15% more CO2 than a gallon of gasoline, so a diesel car only comes out ahead per mile if its mpg is at least that much higher. Compare real cars at their real ratings, not at the same mpg.

The table against real EPA labels

Every listing on fueleconomy.gov shows a tailpipe CO2 figure in grams per mile. Here is how the simple division compares with the listed value for three 2026 models:

The division lands within a few grams of the listing. For a specific car, use the listed number from fueleconomy.gov. For your own driving, use your own mpg: the figure on the label comes from standard tests, and your speed, weather, load and tires change it.

Per trip: from gallons to kilograms

For a single trip, think in gallons. Miles divided by mpg gives the gallons burned, and each gallon is 8.887 kg of CO2. The table shows a few everyday trips at the EPA's typical 22.2 mpg and at the 36 mpg of the hybrid above.

The last row is the EPA's own yearly estimate. At 22.2 mpg and around 11,500 miles a year, a car burns about 518 gallons, and 518 × 8,887 grams is about 4.6 metric tons of CO2. The EPA gives the same figure: a typical passenger vehicle emits about 4.6 metric tons of CO2 per year. A metric ton is 1,000 kg, about 2,205 pounds.

For a real route, the trip fuel cost calculator already works out the fuel a trip needs, in gallons or liters, one way or round trip. Multiply its gallons by 8.887 to get kilograms of CO2, or its liters by 2.35. If your car reports L/100 km or UK mpg, the fuel economy converter turns it into US mpg first. And if you want the answer in pounds, the weight converter handles kilograms to pounds.

Electric cars: zero at the tailpipe, not at the power plant

An all-electric car has no exhaust. The EPA label for electric vehicles says so directly: for electric-only vehicles, the tailpipe greenhouse gas emissions are zero. The same label page adds that these vehicles do cause emissions at the power plant, and that the amount depends on how the electricity is made. The label's greenhouse gas rating counts tailpipe CO2 only, so it cannot show this part.

To put a number on it you need two things: how much electricity the car uses per mile, and how much CO2 the power plants in your area emit per unit of electricity.

• Electricity per mile. The EPA label gives kWh per 100 miles. The 2026 Chevrolet Equinox EV FWD is rated at 31 kWh per 100 miles. The EPA says its MPGe values include charging losses at a Level 2 charger, and MPGe and kWh per 100 miles describe the same energy use (33.7 kWh counts as one gallon), so this is electricity taken from the outlet, not just what reaches the battery.
• CO2 per unit of electricity. The EPA's eGRID database reports the CO2 emitted per megawatt-hour of electricity generated, for the whole US and for 27 grid subregions. The latest edition, eGRID2023, covers 2023 data and was last revised on June 12, 2025. The US average total output rate is 767.2 pounds of CO2 per MWh, which is the same as pounds per 1,000 kWh. EPA recommends using subregion rates rather than state rates.

Multiply the two and you get the CO2 from generating the electricity for each mile. For the Equinox EV at the US average rate: 0.31 kWh × 0.767 lb per kWh × 453.6 grams per pound = about 108 grams per mile. Its gasoline twin, the 2026 Equinox FWD, lists 329 grams per mile at the tailpipe.

The grid varies a lot by region. Here is the same car at the eGRID2023 rates of eight subregions and the US average:

On these numbers the same electric car ranges from about 34 to about 209 grams per mile, depending only on where it is charged. Subregions are not the same as states. EPA's eGRID FAQ says most ZIP codes fall within one subregion, and its Power Profiler tool finds yours from your ZIP code and electric utility.

Keep in mind what this simple calculation leaves out. eGRID rates count emissions at the power plant; EPA's FAQ puts the share of electricity lost on the way to customers, the grid gross loss, at 4.2% for the US in 2023, so slightly more electricity is generated than your car draws. The rates are annual averages, while the mix on the grid changes by hour and season. And neither the EV figure nor the gasoline tailpipe figure includes the emissions of producing the fuel in the first place: mining and transporting coal or gas for power plants, or extracting, refining and shipping gasoline.

For an official estimate that includes those upstream emissions, the EPA and DOE Beyond Tailpipe Emissions Calculator takes a model year, a vehicle and your ZIP code, and shows tailpipe plus upstream emissions next to a gasoline car. Plug-in hybrids sit in between: the DOE's Alternative Fuels Data Center says they have zero tailpipe emissions when running only on electricity, and emit from the tailpipe when the engine runs.

If the units get confusing, the kW vs kWh guide explains why chargers are rated in kW while energy is counted in kWh, and the energy units guide lines up kWh with joules, BTU and calories.

Why lifecycle comparisons give different answers

Tailpipe grams per mile are easy to measure. Comparisons of whole cars are not, and published results differ because they draw the boundary in different places. The DOE's Alternative Fuels Data Center uses three common scopes:

• Tailpipe: only what comes out of the exhaust. Electric cars score zero here.
• Well-to-wheel: all emissions related to fuel production, processing, distribution and use. This adds refineries and power plants.
• Cradle-to-grave: well-to-wheel plus the vehicle itself, from making the car and its battery to recycling or disposal at the end.

Manufacturing is where the two kinds of car differ most. The EPA notes that some studies have found making a typical EV can create more carbon pollution than making a gasoline car, because of the extra energy needed to build the battery. The EPA then concludes that over the vehicle's lifetime, total greenhouse gas emissions from making, charging and driving an EV are typically lower than those of a gasoline car.

The EPA illustrates this with an estimate by researchers at Argonne National Laboratory, made with the lab's GREET model (GREET 2 2021) for model year 2020. That example assumes an EV with a 300-mile range, a gas car at 30.7 mpg, a lifetime of 173,151 miles for both, and the US average grid. The EPA calls the estimates illustrative only and lists what moves the result:

• the specific vehicles being compared, since a small car and a large truck are different cases whatever their fuel;
• battery size and chemistry, since the EPA attributes the extra manufacturing emissions to the battery;
• vehicle lifetime, since manufacturing emissions are spread over every mile the car is driven;
• the electricity grid used to recharge the EV, which the table above shows can vary several times over.

Method choices matter too. eGRID publishes both average rates and non-baseload rates; the US non-baseload rate for 2023 is 1,372 lb per MWh, against 767 for the average. EPA's FAQ describes non-baseload rates as a way to estimate the emissions that could be avoided by projects that displace fossil generation. A study that charges an EV at the non-baseload rate will get a higher figure than one using the average rate, before anything else differs.

When you read a comparison, check four things: the scope (tailpipe, well-to-wheel or cradle-to-grave), the grid rate and the year it describes, the lifetime miles, and which two vehicles are compared. Two honest studies with different answers usually differ in one of these.

Carpooling: the same emissions, divided

A car emits about the same CO2 for a trip whether one person or four are on board, so the CO2 per person falls with every rider. Here is a 30-mile round-trip commute in a 25 mpg car, which burns 1.2 gallons and emits about 10.7 kg of CO2:

The table assumes the fuel economy stays the same with more people aboard. The per-person number is a fair way to share the footprint of a ride, but the total only falls if the carpool replaces trips that would otherwise be driven separately. Two coworkers who each drove 30 miles a day and now share one car cut the combined total roughly in half. A rider who would otherwise have taken the train does not.

The money works the same way. The carpool cost splitter divides fuel, tolls and parking between riders, equally or by the miles each person rides.

Work out your own number

1. Find your real fuel economy. Fill the tank, drive, fill it again and divide miles by gallons. The MPG calculator walks you through the full-tank method.
2. Convert if needed. L/100 km or UK mpg go through the fuel economy converter to US mpg.
3. Grams per mile: 8,887 divided by your mpg for gasoline, 10,180 divided by your mpg for diesel.
4. A trip: get the gallons from the trip fuel cost calculator and multiply by 8.887 kg.
5. An electric car: multiply kWh per mile by your eGRID subregion's rate, or use the Beyond Tailpipe calculator for a figure that includes upstream emissions. The EV charging cost calculator gives the cost side of the same miles.
6. Track it over time. The free mileage log keeps odometer readings and trips, and the car maintenance log keeps the service and tire work that keep fuel economy where it should be.

Emissions and fuel cost come from the same gallons, so they move together. For the money side of gas against electric, the EV vs gas car cost per mile guide works through prices and break-even points.

Frequently asked questions

Sources

• US EPA, Greenhouse Gas Emissions from a Typical Passenger Vehicle (last updated June 3, 2026)
• fueleconomy.gov (US EPA and DOE), How can a gallon of gasoline produce 20 pounds of carbon dioxide?
• fueleconomy.gov, 2026 Chevrolet Equinox FWD, Equinox EV FWD, Hyundai Tucson FWD and Ioniq 5 RWD side by side
• fueleconomy.gov, 2026 Hyundai Tucson Hybrid
• fueleconomy.gov, Learn more about the fuel economy label for electric vehicles
• US EPA, Fuel Economy and EV Range Testing (charging losses in MPGe values)
• US EPA, eGRID Summary Data, eGRID2023 summary tables, revision 2 released June 12, 2025
• US EPA, Frequent Questions About eGRID
• US Department of Energy, Alternative Fuels Data Center, Emissions from electric vehicles
• US EPA, Electric Vehicle Myths (last updated June 10, 2026), with the Argonne GREET 2 2021 example
• fueleconomy.gov (US EPA and DOE), Beyond Tailpipe Emissions Calculator
• NIST Special Publication 811, Guide to the SI, Appendix B.8: conversion factors

Written by Tobias. Updated October 21, 2026.