How We Calculate

Electricity
We calculate emissions from electricity generation based off of state-based figures from Department of Energy’s Energy Information Administration. On average, electricity sources emit 1.297 lbs CO2 per kWh (0.0005883 metric tons CO2 per kWh). State CO2 emissions per kWh may vary greatly in accordance with the amount of clean energy in the energy supply (Vermont, Idaho: .03 lbs/kWh; North Dakota: 2.24 lbs/kWh).

Natural Gas
There are 12.0593 pounds CO₂ per CCF of natural gas. We multiply 12.0593 by the number of CCF consumed annually and divide by 2,205 to get metric tons of CO₂ (Source: US DOE 1605(b) Voluntary Reporting of Greenhouse Gases Program.)

US avg.: In 2005 62.5 million households used natural gas. Collectively, they used 4,838 billion cubic feet of natural gas annually, or 774.08 CCF (approximately 812 therms) per household or 296.58 CCF (approximately 311 therms) per person per household using natural gas. (Source: Energy Information Agency, US Census Bureau.)

Heating Oil
There are 22.384 pounds of CO₂ per gallon of heating oil (diesel fuel). We multiply 22.384 by the number of gallons of heating oil consumed annually and divide by 2,205 to get metric tons of CO₂ per gallon. (Source: US DOE 1605(b) Voluntary Reporting of Greenhouse Gases Program.)

US avg.: In 2004, 5,997 million gallons of heating oil were consumed by 8.1 million households, resulting in an average of 740.37 gallons per household or 283.67 gallons per person per household using heating oil. (Source: Energy Information Agency. Volume; Households.)

Vehicles
Unleaded gasoline has 8.87 kg (19.56 lbs) of CO₂ per gallon. By dividing number of miles driven by miles per gallon, we get the number of gallons of gasoline consumed annually. We multiply this by 8.87 and divide by 1,000 to get metric tons of CO₂ (Source: US DOE 1605(b) Voluntary Reporting of Greenhouse Gases Program.)

US avg.: Automobiles fuel efficiency (MPG) varies widely so averages are not all that useful. It is useful for you to have an idea of your own car’s fuel economy. The average fuel economy for cars sold in 2005 is about 25.2 MPG (Source: National Highway Traffic Safety Administration.)

The Department of Transportation's MOBILE 6.2 model, used by regional governments to model air quality, uses a fleet average (all cars, old and new) of 20.3 mpg. (Source: EPA.)

Metric users: To convert liters per 100 km, the metric standard, to CO₂, do the following: kilometers per year * 0.62 and enter it in the miles driven per year box. There are 3.79 liters per gallon. Hint: 7.58 l/100km = 30mpg.

British users: Take your MPG and multiply by .83 to get US MPG (Source: Digital Dutch web converter.) In 2001, the average distance driven by US drivers was 13,785 miles (Source: Federal Highway Administration, page 41.)

Air Travel
CO₂ emissions in air travel vary by length of flight--ranging from .24 kg CO₂ per passenger mile for short flights down to .18 kg CO₂ per passenger mile for long flights. Our calculator allows the user to take the issue of radiative forcing into account. (Sources: Emissions factor based on 2006 data collected in the United Kingdom available from the The World Resources Institute. For more information on air travel-related radiative forcing, please see this IPCC document.)

US avg: We do not have accurate figures for numbers of miles flown per flyer in the United States. Using per capita figures would be misleading because not every person flies. We would welcome any information that would help us determine an accurate average.

Meals
The average person's diet contributes 455.41 kg CO₂e to the atmosphere each year. By dividing by 365, it is deduced that a person emits, on average, 1.25 kg CO₂e a day from their meals. This calculation is based on a non-vegetarian diet. The emissions for food preparation are not included in this calculation. (Source: Wired Magazine.)

Electricity
Emissions factors for electricity by your monthly bill are based on state based figures from the Department of Energy’s Energy Information Administration to get the state-by-state prices for energy, and the emissions factors are generated from the Department of Energy’s Energy Information Administration.

Fleet
Fleet emissions cars assume the national average of 25.2 mpg and the emissions factor of 19.564 lbs CO2 per gallon of gasoline consumed. Fleet emissions deliver vans and trucks assume an average of 7.8 mpg (Source: EERE) and the emissions factor of 22.384 lbs CO2 per gallon of diesel consumed. Fleet emissions big rigs assume an average of 5.3 mpg and the emissions factor of 22.384 lbs CO2 per gallon of diesel consumed.

Employee Travel
All travel emissions factors sourced from WRI.

• Short flights are calculated to be 500 miles round-trip with emissions of 0.53 lbs CO2 per passenger mile
• Medium flights are calculated to be 1,500 miles round-trip with emissions of 0.42 lbs CO2 per passenger mile
• Long flights are calculated to be 4,000 miles round-trip with emissions of 0.397 lbs CO2 per passenger mile
• Train trips are calculated 0.35 lbs CO2 per passenger mile
• Bus trips are calculated at 0.18 lbs CO2 per passenger mile

Employee Commute
A ll emissions figures from WRI.

• Commute by Car – assumes 25.2 mpg fuel efficiency for the vehicle, 19.564 lbs CO2 per gallon of gas consumed and a two way commute 245 days a year.
• Commute by Transit – assumes a two way commute 245 days a year, with 0.37 lbs CO2 emitted per mile.