How was your carbon footprint calculated?

Introduction

Calculating an individual’s impact on the climate is not an exact science. The calculations below, therefore, try to incorporate the most up-to-date references and data available. The most prudent assumptions have been made, and objective sources of information have been used for citation purposes. Where they are applicable, conservative estimates have been made.

Home Emissions

To calculate Estimated home emissions, the calculator adds together the amount of emissions resulting from electricity and natural gas usage, based on the selected state’s average consumption and residence type and size.
  • Electricity: the calculator multiplies the selected state’s yearly average consumption of kilowatt hours (kWh) per household by a percentage, [1] 50%, 75%, or 100% based on the type of residence selected: apartment, townhouse or rowhouse, or single family house, respectively. The product is multiplied by a factor of 0.8, 1.0, or 1.2, based on the size of the residence selected. This number is then multiplied by the selected state’s electricity emissions intensity (lbs. of CO2 emitted per kWh generated)*. This results in the total amount of pounds of carbon dioxide, which is divided by 2,205, the number of pounds in a metric ton, to calculate metric tons.

* Emissions intensity is calculated by measuring the amount of pounds of carbon dioxide that is emitted as a result of generating one kilowatt hour of electricity; this figure varies considerably by state depending on the types of resources, e.g. coal, natural gas, wind, hydro, etc. that are used to generate the electricity consumed. A state, for example, that relies more on electricity that is generated from hydro power will have a lower intensity than a state that relies heavily on coal for power generation. For the purposes of this calculator, each state has been assigned a particular emissions rate (intensity) based on a "subregion" location within the US Environmental Protection Agency’s Emissions & Generation Resource Integrated Database (eGRID). See the footnote for more details.[2]

  • Natural Gas: the calculator multiplies the selected state’s yearly average consumption of therms per household by a percentage, [3] 50%, 75%, or 100% based on the type of residence selected: apartment, townhouse or rowhouse, or single family house, respectively. The product is multiplied by a factor of 0.8, 1.0, or 1.2, based on the size of the residence selected. The result is then multiplied by 12.0593, [4] the amount of pounds of carbon dioxide that is emitted as a result of burning one therm of natural gas. To calculate metric tons, this number is divided by 2,205.

To calculate Exact home emissions, the calculator adds together the amount of emissions resulting from your electricity, natural gas, heating oil and propane usage.

  • Electricity: the calculator multiplies the entered number of kilowatt hours of electricity consumed in a year by the electricity emissions intensity (lbs. of CO2 emitted per kWh generated) of the state where the residence is located (see explanation above and corresponding endnote). This amount, total pounds of CO2 emitted per year from your electricity consumption, is then divided by 2,205, the number of pounds in a metric ton.
  • Natural Gas: the calculator multiplies the entered number of therms of natural gas consumed in a year by 12.0593, [5] the amount of pounds of carbon dioxide that is emitted from burning one therm of natural gas. The product is divided by 2,205 to calculate metric tons.
  • Heating oil: the calculator multiplies the entered number of gallons of heating oil consumed in a year by 22.384, [6] the amount of pounds of carbon dioxide that is emitted from burning one gallon of heating oil. The product is divided by 2,205 to calculate metric tons.
  • Propane: the calculator multiplies the entered number of gallons of propane consumed in a year by 12.669, [7] the amount of pounds of carbon dioxide that is emitted from burning one gallon of propane. The product is divided by 2,205 to calculate metric tons.
If you are using an Eco-Metro guide, the amount of carbon dioxide resulting per square foot (lbs CO2/ sq ft) is calculated as follows:
  1. Add together the total amount of carbon dioxide (lbs) resulting from electricity and natural gas usage per household.
  2. Divide by the US median household size (sq ft), which is 1,758 sq ft according to US Census Bureau.[a]


Auto Emissions

For each vehicle, to calculate Estimated auto emissions, the calculator divides the average number of miles an American drives in a year, 12,000, [8] by the estimated fuel efficiency (mpg) of the vehicle type that is selected.

hybrid passenger car = 50 mpg[9]
hybrid truck or hybrid SUV = 25 mpg[10]
diesel car = 35 mpg[11]
small car = 26 mpg[12]
mid-size car = 24 mpg[13]
large car = 22 mpg[14]
small SUV or small truck = 21 mpg[15]
midsize SUV or midsize truck = 20 mpg[16]
large SUV or large truck = 17 mpg[17]
van = 20 mpg[18]
motorcycle = 50 mpg[19]
no specific classification = 21 mpg[20]

The quotient is multiplied by 19.36, [21] the amount of pounds of carbon dioxide that is emitted as a result of burning one gallon of gasoline. The product is then divided by 2,205, the number of pounds in a metric ton.

For each vehicle, to calculate Exact auto emissions, the calculator divides the total number of miles driven in a year by the miles per gallon (mpg) or fuel efficiency of the vehicle driven. The quotient is multiplied by 19.36, [22] the amount of pounds of carbon dioxide that is emitted as a result of burning one gallon of gasoline. The product is then divided by 2,205, the number of pounds in a metric ton.

Air Travel Emissions

To calculate Estimated air travel emissions, the calculator multiplies the entered estimated number of hours flown in a year by 414.65, [23] the average number of miles flown per hour of air travel. The product is multiplied by 1.3068, [24] which is the total climate impact of one air-passenger mile, expressed in pounds of carbon dioxide. The result is then divided by 2,205, the number of pounds in a metric ton.

To calculate Exact air travel emissions, the calculator multiplies the entered total number of miles flown in a year by 1.3068, [25] which is the total climate impact of one air-passenger mile, expressed in pounds of carbon dioxide. The result is then divided by 2,205, the number of pounds in a metric ton.

Average American Emissions

The carbon footprint of the average American is calculated by adding together the average home, auto, and air travel emissions.

  • Home
    • Electricity: The average American household consumes 10,892 kWhs per year. [26] To calculate the number of metric tons associated with this consumption, the calculator multiplies this number by 1.3925, [27] the national average of the amount of pounds of carbon dioxide that are emitted as a result of generating one kWh of electricity (emissions intensity). This equals 15,167.17 lbs. of CO2 per year from electricity consumption, which is then divided by 2,205 to convert to metric tons: 6.88 tons.
    • Natural Gas: The average American household consumes 781.91 therms per year. [28] So to calculate the number of metric tons associated with this consumption, the calculator multiplies this number by 12.0593, the amount of pounds of carbon dioxide that is emitted as a result of burning one therm. [29] This equals 9,429.28 lbs. of CO2 per year from natural gas consumption, which is then divided by 2,205 to convert to metric tons: 4.28 tons.

  • Auto
    • The average number of miles an American drives in a year is 12,000 miles. [30] This is divided by the average fuel efficiency of the American vehicle fleet, 21 mpg, [31] and then multiplied by 19.36, the amount of pounds of carbon dioxide that is emitted from burning one gallon of gasoline, [32] which equals 11,062.86 lbs. of CO2. After dividing this figure by 2,205, the result is 5.02 metric tons.
  • Air
    • It has been estimated that the average American flies 1,055 miles per year. [33] To calculate the corresponding amount of emissions, the calculator multiplies this number by 0.968, the total climate impact of one air-passenger mile, [34] expressed in pounds of carbon dioxide. The result, 1,015.75 lbs of CO2 equivalent, divided by 2,205 equals 0.46 metric tons.


[1] US Department of Energy, Energy Information Administration, “Electric Sales, Revenue, and Average Price 2004,” http://www.eia.doe.gov/cneaf/electricity/esr/esr_sum.html; Table 5, “U.S. Average Monthly Bill By Sector, Census Division and State,” http://www.eia.doe.gov/cneaf/electricity/esr/table5.xls. Each state’s monthly consumption average in the table was multiplied by 12 to calculate yearly average consumption.

[2] See U.S. Environmental Protection Agency, “eGRID2006 Version 2.1: Year 2004 Summary Tables,” April 2007, p.3, http://www.epa.gov/cleanenergy/egrid/pdfs/eGRID2006V2_1_Summary_Tables.pdf.
Each state has been assigned to one of the 26 eGRID subregions, illustrated in the document, and therefore to that subregion’s corresponding emissions rate. For any state that lies completely within the boundaries of a subregion, that subregion was assigned to the state. For a state that lies within the boundaries of multiple subregions, it was assigned to the subregion with the lowest emissions rate (lbs. CO2/kWh), unless it is obvious that most of the population of the state lives in the more emissions intensive subregion, e.g. Alaska. (A Census Bureau Population Density Map based on counties was used to determine this, see http://www.census.gov/popest/gallery/maps/popdens06.html.) Interestingly, the emissions rates of these adjoining regions within a state do not vary by much, and the more densely populated areas of almost all of the states correspond to the less intensive subregion.

[3] US Department of Energy, Energy Information Administration, Natural Gas Annual 2004, http://www.eia.doe.gov/oil_gas/natural_gas/data_publications/natural_gas_annual/nga.html; see Table 16. “Natural Gas Delivered to Consumers by State and Sector, 2000-2004,” http://www.eia.doe.gov/pub/oil_gas/natural_gas/data_publications/natural_gas_annual/current/pdf/table_016.pdf. Yearly average consumption for each state was calculated by dividing the residential volume (million cubic feet) consumed by the number of residential consumers, and then dividing that result by 100, which converts the number of cubic feet into therms.

[4] US Department of Energy, Energy Information Administration, Voluntary Reporting of Greenhouse Gases Program (Emission Coefficients), “Fuel and Energy Source Codes and Emission Coefficients,” http://www.eia.doe.gov/oiaf/1605/factors.html. One therm is equivalent to 100 cubic feet of natural gas.

[5] Ibid.

[6] Ibid.

[7] Ibid.

[8] US Environmental Protection Agency, Office of Transportation and Air Quality, “Emission Facts: Greenhouse Gas Emissions for Typical Passenger Vehicle,” February 2005, p.4, http://www.epa.gov/otaq/climate/420f05004.pdf.

[9] Heavenrich, Robert M., US EPA, Office of Transportation and Air Quality, “Light-Duty Automotive Technology and Fuel Economy Trends: 1975 Through 2005,” July 2005, Table 10, pg. 38, http://www.epa.gov/otaq/cert/mpg/fetrends/420r05001.pdf. Fuel efficiency was calculated by taking the average of the adjusted 55/45 mpg for model year (MY) 2005 hybrid cars.

[10] Ibid., the average of the adjusted 55/45 mpg for MY2005 hybrid trucks.

[11] Ibid., the average of the adjusted 55/45 mpg for MY2005 diesel cars.

[12] Heavenrich, Table 14, pg. 50, http://www.epa.gov/otaq/cert/mpg/fetrends/420r05001.pdf. Figure represents the average adjusted mpg of the vehicle from the table, conservative rounding. See also, Heavenrich, Robert M., US EPA, “Light-Duty Automotive Technology and Fuel Economy Trends: 1975 Through 2006,” July 2006, Appendix F, http://www.epa.gov/OTAQ/cert/mpg/fetrends/420r05001f.pdf.

[13] Ibid., figure represents the average adjusted mpg of the vehicle from the table, conservative rounding.

[14] Ibid.

[15] Ibid.

[16] Ibid.

[17] Ibid.

[18] Ibid.

[19] US Department of Transportation, Bureau of Transportation Statistics, “Table 4-11: Passenger Car and Motorcycle Fuel Consumption and Travel,” 1960-2004, http://www.bts.gov/publications/national_transportation_statistics/html/table_04_11.html. Figure was calculated by dividing the total number of miles traveled via motorcycle in 2004 by the number of gallons of fuel consumed by motorcycles.

[20] Heavenrich, “Light-Duty Automotive Technology and Fuel Economy Trends: 1975 Through 2005,” July 2005, Table 14, pg. 50, http://www.epa.gov/otaq/cert/mpg/fetrends/420r05001.pdf. The average adjusted fuel economy for all model year 2005 vehicles was 21.0 mpg.

[21] US Department of Energy, Office of Policy and International Affairs, “Technical Guidelines: Voluntary Reporting of Greenhouse Gases (1605(b)) Program,” March 2006, Table 1.D.1, p. 64,

http://www.eia.doe.gov/oiaf/1605/TechnicalGuidelines_March2006.pdf.

[22] Ibid.

[23] U.S. Department of Transportation, Bureau of Transportation Statistics, “U.S. Air Carrier Traffic Statistics,” http://www.bts.gov/xml/air_traffic/src/datadisp.xml; table generated on 8/18/2006, figure was calculated by dividing the total number of scheduled System Revenue Aircraft Miles Flown in 2005, 7,915,129,000 miles, by the total number of scheduled System Revenue Aircraft Hours (Airborne) in 2005, 19,088,831 hours.

[24] In 2005, total Revenue Passenger Miles flown (scheduled flights only for domestic and international flights of US certificated airlines) was 779,004,706,880 miles (source: U.S. Department of Transportation, Bureau of Transportation Statistics; TranStats, Air Carrier Summary: Schedule T-1, http://www.transtats.bts.gov/Fields.asp?Table_ID=264; table generated 8/18/2006). Total jet fuel consumed (scheduled flights only for domestic and international flights) in 2005 was 18,062,449,227 gallons (source: U.S. Department of Transportation, Bureau of Transportation Statistics, “Airline Fuel Cost and Consumption – 2005,” http://www.bts.gov/xml/fuel/report/src/monthrep.xml?styyyy=2005; table accessed 8/18/2006). Divide these two numbers to get 43.13 Revenue Passenger Miles per gallon of jet fuel burned. This figure is then divided into 20.88, the amount of pounds of carbon dioxide that is emitted when one gallon of jet fuel is burned (see US DOE “Technical Guidelines: above), to get 0.484 lbs. of CO2 per Revenue Passenger Mile. A conservative RFI (radiative forcing index) of 2.7 was then applied to account for the more accurate global warming impact of air travel, which includes the impact of greenhouse gases in addition to CO2, such as nitrous oxide, and contrails; see http://www.grida.no/climate/ipcc/aviation/064.htm. Thus, 2.7 multiplied by 0.484 equals 1.3068 lbs of CO2 equivalent emitted for each Revenue Passenger mile traveled.

[25] See endnote above.

[26] US Department of Energy, Energy Information Administration, “Electric Sales, Revenue, and Average Price 2004,” http://www.eia.doe.gov/cneaf/electricity/esr/esr_sum.html; Table 5, “U.S. Average Monthly Bill By Sector, Census Division and State,” http://www.eia.doe.gov/cneaf/electricity/esr/table5.xls. The monthly US consumption average in the table was multiplied by 12 to calculate yearly US average consumption.

[27] U.S. Environmental Protection Agency, Climate Leaders Greenhouse Gas Inventory Protocol: Core Module Guidance, “Indirect Emissions from Purchases/Sales of Electricity and Steam,” October 2004, Appendix B, http://www.epa.gov/climateleaders/docs/indirectelectricityguidance.pdf.

[28] US Department of Energy, Energy Information Administration, Natural Gas Annual 2004, http://www.eia.doe.gov/oil_gas/natural_gas/data_publications/natural_gas_annual/nga.html; see Table 16. “Natural Gas Delivered to Consumers by State and Sector, 2000-2004,” http://www.eia.doe.gov/pub/oil_gas/natural_gas/data_publications/natural_gas_annual/current/pdf/table_016.pdf. Yearly average consumption for the US was calculated by dividing the 2004 residential volume (million cubic feet) consumed by the number of 2004 residential consumers, and then dividing that result by 100, which converts the number of cubic feet into therms.

[29] US Department of Energy, Energy Information Administration, Voluntary Reporting of Greenhouse Gases Program (Emission Coefficients), “Fuel and Energy Source Codes and Emission Coefficients,” http://www.eia.doe.gov/oiaf/1605/factors.html. One therm is equivalent to 100 cubic feet of natural gas.

[30] US Environmental Protection Agency, Office of Transportation and Air Quality, “Emission Facts: Greenhouse Gas Emissions for Typical Passenger Vehicle,” February 2005, p.4, http://www.epa.gov/otaq/climate/420f05004.pdf.

[31] Heavenrich, “Light-Duty Automotive Technology and Fuel Economy Trends: 1975 Through 2005,” July 2005, Table 14, pg. 50, http://www.epa.gov/otaq/cert/mpg/fetrends/420r05001.pdf. The average adjusted fuel economy for all model year 2005 vehicles was 21.0 mpg.

[32] US Department of Energy, Office of Policy and International Affairs, “Technical Guidelines: Voluntary Reporting of Greenhouse Gases (1605(b)) Program,” March 2006, Table 1.D.1, p. 64,

http://www.eia.doe.gov/oiaf/1605/TechnicalGuidelines_March2006.pdf.

[33] U.S. Department of Transportation, Bureau of Transportation Statistics; TranStats, Air Carrier Summary: Schedule T-1, http://www.transtats.bts.gov/Fields.asp?Table_ID=264. Total Revenue Passenger Miles flown (Scheduled flights only for Domestic and International) in 2005 was 779,004,706,880 miles. Total Revenue Passenger Enplanements (Scheduled flights only for Domestic and International) in 2005 was 738,571,388 enplanements. Divide these two numbers to get 1,055 miles traveled per enplanement. We assume the average American flies only once per year.

[34] See Endnote 24.

[a] US Census Bureau, Housing and Household Economic Statistics Division, 2005 American Housing Survey for the United States, http://www.census.gov/hhes/www/housing/ahs/ahs05/tab1a3.html.

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