Carbon Footprint Calculator

Estimate the greenhouse gases a household sends out from electricity, gasoline and natural gas using EPA factors.

What it does

A carbon footprint is a way of putting a number on the greenhouse gases that come out of your own use of energy and fuel. The most useful version for a household is a simple screen built on published factors: electricity from the grid factor for your area, gasoline from the combustion factor for motor fuel, and natural gas from the factor for gas.

The Environmental Protection Agency publishes those factors. The electricity numbers come from eGRID, which maps the generation mix of each power region, so the same 350 kilowatt hours produce very different emissions depending on where you live. A coal heavy grid emits roughly twice as much per kilowatt hour as a grid with a lot of wind and solar.

For fuels the EPA publishes combustion factors: 8.887 kilograms of carbon dioxide for each US gallon of motor gasoline, and 53.06 kilograms of carbon dioxide per million British thermal units, which works out at 5.306 kilograms per therm of natural gas.

The result is a screening estimate, not an audited inventory. It counts carbon dioxide from burning fuel and the carbon dioxide equivalent of the electricity you use. It leaves out methane and nitrous oxide from fuel, the emissions from refining and delivery, and anything you buy that was made for you.

It is still a useful number because it points at the biggest lever. If gasoline is half the total, driving less moves the number more than anything else you could do this year.

How to use

Choose imperial or metric units for the fuel you buy.
Enter your monthly electricity use in kilowatt hours from your bill.
Enter the grid factor for your area. The US average from eGRID2023 is 0.3497 kg CO2e per kWh.
Enter the gasoline you burn each month.
Enter the natural gas you use each month in therms.
Read the total for the month, the total for the year and the gasoline equivalent.

Formula

Emissions = activity data x emission factor. Electricity: kWh x kg CO2e per kWh. Gasoline: gallons x 8.887 kg CO2 per gallon. Natural gas: therms x 5.306 kg CO2 per therm.

E: Emissions from one source in kilograms of CO2 or CO2e.
A: Activity data, such as kilowatt hours, gallons or therms used in the period.
F: Emission factor for that activity, published by EPA.
Grid factor: Kilograms of CO2e per kilowatt hour from eGRID for your power region.

The electricity factor is a CO2e figure taken from eGRID2023 total output rates, so it already includes the other greenhouse gases from power generation. The two fuel factors are carbon dioxide from combustion only, so the total mixes two conventions. Both leave out upstream emissions such as refining, and the gasoline factor does not vary with the vehicle or its model year.

Worked example

Example: 350 kWh, 40 gallons and 30 therms a month

Defaults: imperial units, 350 kWh of electricity, a grid factor of 0.3497, 40 US gallons of gasoline and 30 therms of natural gas each month.

Electricity: 350 kWh x 0.3497 kg per kWh = 122.4 kg CO2e.
Gasoline: 40 gallons x 8.887 kg per gallon = 355.5 kg CO2.
Natural gas: 30 therms x 5.306 kg per therm = 159.2 kg CO2.
Monthly total: 122.4 + 355.5 + 159.2 = 637.1 kg.
Yearly total: 637.1 x 12 = 7,645.2 kg, which is 8.43 US tons or 7.64 metric tonnes.
Gasoline equivalent: 637.1 / 8.887 = 71.7 gallons of gasoline.
The tool shows 122.4 kg, 355.5 kg, 159.2 kg, 637.1 kg, 8.43 US tons and 71.7 gallons.

Reference table

eGRID2023 output emission rates for common grid areas
Grid area	lb CO2e per MWh	kg CO2e per kWh
United States average	770.884	0.3497
CAMX, WECC California	429.983	0.1950
ERCT, ERCOT all	736.629	0.3341

Limits

Counts only electricity, gasoline and natural gas, so flying, deliveries, food and goods are missing.
Uses combustion factors for fuels, so methane and nitrous oxide from fuel are left out.
Assumes the same use every month when it turns a month into a year.
The grid factor is regional, so a city on a cleaner local grid will do better than the regional number.

Common mistakes

Using the emission factor of the cheapest power source instead of the factor for the grid you actually buy from.
Adding kilowatt hours of electricity and therms of gas without converting them to the same unit first.
Treating the result as a complete carbon footprint when it leaves out everything you buy.
Mixing metric and imperial entries, for example entering gallons in the liter box.
Forgetting that the fuel figures are carbon dioxide while the grid figure is carbon dioxide equivalent.

Try it yourself

Quick checks. Answers sit tucked under each question.

A household uses 500 kWh a month on a grid with 0.1950 kg CO2e per kWh and drives 60 US gallons a month. What is the monthly total?

Electricity is 500 x 0.1950 = 97.5 kg and gasoline is 60 x 8.887 = 533.2 kg, so the total is 630.7 kg a month, which is 7.57 tonnes a year.

How much would the example household save in carbon by moving from a 0.3497 grid factor to 0.1950?

Electricity would fall from 350 x 0.3497 = 122.4 kg to 350 x 0.1950 = 68.3 kg, a drop of 54.1 kg a month, or about 649 kg a year.

A household burns 45 gallons of gasoline and 40 therms of gas a month with no electricity. What is the monthly total?

Gasoline is 45 x 8.887 = 399.9 kg and gas is 40 x 5.306 = 212.2 kg, so the total is 612.2 kg a month.

Questions

What is the average US household carbon footprint?

This tool does not claim a national average because the number depends on the grid and the car. A household on 350 kWh, 40 gallons and 30 therms lands near 637 kg a month, or 7.64 tonnes a year, and most of the spread comes from electricity and driving.

Which source contributes the most?

It depends where you live. Gasoline usually wins because a gallon releases 8.887 kg directly. Electricity takes over in regions with a coal heavy grid, where the kilogram per kilowatt hour is more than twice the national average.

Where do I find the grid factor for my area?

The EPA eGRID data lists an output rate for each power region, and the table on this page shows three examples. Use the rate for your region rather than the national average when you have it.

Does this include the emissions from making the fuel?

No. The factors are combustion factors, so they cover what leaves the tailpipe or the power plant. Refining, shipping and mining are not counted here.

What is a therm?

A therm is 100,000 British thermal units of energy, and it is the unit most North American gas meters use. One therm equals 29.3 kWh of energy.

How much would a solar panel cut this total?

Every kilowatt hour of electricity you make yourself removes 0.3497 kg from the total on the US average grid. A household using 350 kWh a month that covers half of that with panels cuts about 61 kg a month, or 735 kg a year.

Sources

How this page was checked. The formula above was matched against the cited sources, and the worked example was run through the tool on this page before publishing. If you spot an error, contact us so we can fix it and note the correction.