What is your household's carbon footprint?

What the number means

Your carbon footprint is the amount of greenhouse gas your household's energy use puts into the air in a year, written as carbon dioxide equivalent (CO2e). Methane and nitrous oxide are counted by their 100-year global warming potential, 28 and 265 in the EPA's current factor tables, so everything lands in one unit: metric tons. The result is a bill-based estimate of the parts of your life that arrive as meters, pumps and tickets. It is not a full life-cycle audit.

The method, variable by variable

Electricity = monthly kWh × 12 × grid factor. The default factor is the EPA's eGRID2023 national output rate, 770.884 lb CO2e/MWh, or 0.3497 kg per kWh. Natural gas = monthly therms × 12 × 5.311 kg: that is the EPA's 53.06 kg CO2 per million Btu plus methane and nitrous oxide, on 0.1 million Btu per therm. Driving = miles ÷ mpg × 8.887 kg per gallon of gasoline. Flying = round trips × 2 × miles each way × people × the per-passenger-mile factor for that trip length: 0.209 kg for under 300 miles, 0.13 kg for 300 to 2,300 miles, 0.164 kg for 2,300 miles and more.

Worked example

A household of three uses 900 kWh and 40 therms a month, drives 12,000 miles a year at 25 mpg, and two adults take two round trips of 1,200 miles each way. Electricity: 900 × 12 × 0.3497 = 3,776 kg. Gas: 40 × 12 × 5.311 = 2,549 kg. Car: 12,000 ÷ 25 × 8.887 = 4,266 kg. Flights: 9,600 passenger-miles × 0.1301 = 1,249 kg. The total is 11,841 kg, or 11.8 metric tons a year: 3.9 tons per person, about 28% of the roughly 14-ton US average per person. Remember that the national average includes every factory and truck in the country, so it is a scale, not a target.

Limits of this method

Grid factors are averages. The EPA output rate is the mean emission of all power generated in the region and year; it is not the marginal plant that runs when you add a load, and it is based on generation, without the losses in power lines. Hourly and regional data can differ from the national value by a factor of three or more, as the EPA's own subregion table shows. Airline factors are old and partial. The Emission Factors Hub uses Defra figures from the 2022 guidelines, based on 2018 activity data, and says so; they leave out contrails and other high-altitude effects. The car line is CO2 only. Methane and nitrous oxide from a tailpipe are small, under one percent of a gasoline car's total in the EPA's per-mile figure, so they are left out. Electric cars are not modeled: put their charging in the electricity line and leave the car blank.

Common mistakes

Entering a yearly electricity total in the monthly box overstates that line twelvefold. Mixing up therms and cubic feet changes the gas line tenfold, since one therm is about 100 cubic feet. Counting one-way miles for a round trip halves the flights; the field asks for miles each way and counts the return. And comparing a household total with a per-person average is a trap: always read the per-person line.

Questions

How is a household carbon footprint calculated?

Each activity is turned into an amount of fuel or electricity, and that amount is multiplied by an emission factor: kilograms of carbon dioxide equivalent (CO2e) per unit. The calculator adds four sources: grid electricity, natural gas, gasoline for the car and flights. The factors come from the EPA: 0.35 kg CO2e per kWh for the average US grid (eGRID2023), 5.31 kg per therm of natural gas, 8.887 kg per gallon of gasoline, and 0.13 to 0.21 kg per passenger-mile in the air, depending on trip length.

How much CO2 does the average American produce?

Energy-related CO2 emissions in the United States were 4,789 million metric tons in 2024 according to the EIA. Divided by about 340 million residents, that is roughly 14 metric tons per person. The figure covers all energy use, including factories, offices, freight and power plants, so it is larger than what a household's own bills explain. The calculator compares your per-person result with it for a rough scale, not as a target.

Which electricity emission factor should I use?

The default is the national average from the EPA's eGRID2023 data: 770.884 pounds of CO2e per megawatt-hour. Grids differ a lot: the EPA's own subregion table runs from about 242 lb/MWh in upstate New York to about 1,240 lb/MWh in the SERC Midwest region (SRMW), and over 1,500 in Puerto Rico. If you know your region's rate, from the EPA's Power Profiler or your utility, type it in the grid field. A household on a clean grid will see electricity shrink to a small part of the total; on a coal-heavy grid it can be the largest part.

Why not include food and shopping?

Food, goods and services are a large part of a person's footprint, but the numbers depend on what is bought, where it was made and how it was shipped, and no single public EPA factor covers them. A figure invented to fill the gap would only look precise. This page stays with the four sources where an official factor exists, so every line of the result can be traced to a document.

How is this different from the driving CO2 calculator?

The driving CO2 calculator takes one car and one trip or year of driving. This page puts the car next to the home's electricity and gas and next to flights, so you can see which of them moves the total. If you only want the emissions of a single trip, use the driving CO2 calculator.

Do flights have an extra effect that is not counted?

Yes. The EPA's air-travel factors are carbon dioxide, methane and nitrous oxide from burning the fuel, based on Defra data from 2022; they do not include the additional warming from contrails and high-altitude effects that some other tools add. Treat flight figures here as a lower bound.

How can I lower the number the fastest?

Look at the table of shares first and attack the biggest line. Swapping a gasoline car for a more efficient one cuts the car line in proportion to the mpg ratio (25 mpg to 50 mpg halves it), and burning less gas for heat cuts the gas line one-for-one. Enter the new numbers and compare the totals instead of trusting a rule of thumb.

Sources: EPA eGRID2023 summary data, revision 2, June 12, 2025 (US total output emission rate CO2e 770.884 lb/MWh); EPA, Emission Factors for Greenhouse Gas Inventories, January 15, 2025 edition (Table 1 stationary combustion, Table 10 business travel, Table 11 global warming potentials); EPA, Greenhouse Gases Equivalencies Calculator, calculations and references; EIA, Energy-Related CO2 Emissions, Table 1. All read October 27, 2026. For one car, see the driving CO2 calculator; to price your power see the electricity cost calculator and the solar panel calculator; fuel costs: heating cost calculator. How we check our calculators.