Our Methodology

Assumptions
Emissions per MMBtu = 0.058 tons of CO₂
Average Household = 5 tons of CO₂ per year
Average People per Household = 2.6
Average U.S. Household Size = 2,066 square feet
Apartment Building with 5+ Units = 850 square feet
Apartment Building with 2-4 Units = 1,400 square feet
Mobile Home = 1,060 square feet
Single Family Home (Attached) = 2,375 square feet
Single Family Home (Detached) = 2,550 square feet
International Electricity Consumption = 1.5 lbs/kwh
Metric Tons of CO₂ = lbs/2204
Vegan Diet = 2.0 tons of CO₂
Vegetarian Diet = 2.7 tons of CO₂
Mostly Vegetarian Diet = 3.0 tons of CO₂
Omnivorous Diet = 3.8 tons of CO₂

Simple Mode

• Your Household Emissions = Energy Consumption by Household Type and Size x Emissions per MMBtu
  
• Your Personal Contribution = Household Emissions / Number of Residents

Detail Mode

• Your Household Emissions = Electricity Emissions + Natural Gas Emissions + Heating Oil Emissions + Propane/LPG Emissions + Wood Emissions
  
• Your Personal Contribution = Household Emissions / Number of Residents
  
• Electricity Emissions = {[Your Monthly Electricity Usage x Emissions per kWh of Electricity by State] / 2204} x 12
  
• Natural Gas Emissions = {[Your Monthly Natural Gas Usage x Emissions per Therm of Natural Gas] / 2204} x 12
  
• Heating Oil Emissions = [Your Yearly Heating Oil Usage x Emissions per Gallon of Heating Oil] / 2204
  
• Propane/LPG Emissions = [Your Yearly Propane/LPG Usage x Emissions per Gallon of Propane/LPG] / 2204


• Wood Emissions = Your Yearly Wood Use x Emissions per Cord of Wood

Diet
Estimating the carbon footprint of your food and beverage choices is perhaps the most difficult of all calculations. Emissions vary considerably depending on how food is grown, processed, packaged, shipped, etc. It takes roughly 100,000 liters of water to produce 1 kilogram of beef, for example, whereas it takes 900 liters of water to produce 1 kilogram of grain. Replacing one beef meal with a vegetarian option just once a week can, on average, save more than 40,000 gallons of water and prevent 300 pounds of greenhouse gas emissions from entering the atmosphere per year. 

Assumptions
Emissions per Gallon of Gasoline = 0.0089 tons of CO₂
Average Annual Miles per Household = 11,100
Per Capita Miles Driven in 2004 = 9,941
Average Vehicle Trip = 10 miles
Average Fuel Economy = 22 miles per gallon

Simple Mode

• Your Car Travel Emissions = [Miles Driven per Year / Average Fuel Economy by Car Class and Year] x Emissions per Gallon of Gasoline

Detail Mode

• Your Car Travel Emissions = [Miles Driven per Year / Your Fuel Economy] x Emissions per Gallon of Gasoline

Our default assumption is that you’re traveling on commercial aircraft. But for those of you who travel by private jet, we have provided additional data here to more accurately calculate your flight emissions. Our “Emissions per Private Jet Flight Mile” variable is based on the emissions data of the Beechcraft King Air jet model, which is responsible for 49.7 metric tons of CO₂ at 5,000 miles.

Assumptions
Short Roundtrip Distance = 800 miles
Long Roundtrip Distance = 3,000 miles
Emissions per Commercial Air Passenger Mile = 0.00041 tons of CO₂
Emissions per Private Jet Flight Mile = 0.0099 tons of CO₂
Emissions per Person per Hotel Night = 0.0136 tons of CO₂

Simple Mode

• Your Air Travel Emissions = Average Short Roundtrip Emissions + Average Long Roundtrip Emissions
  
• Short Roundtrip Emissions = Number of Yearly Short Roundtrip Flights x [Emissions per Commercial Air Passenger Mile OR Emissions per Private Jet Flight Mile]
  
• Long Roundtrip Emissions = Number of Yearly Long Roundtrip Flights x [Emissions per Commercial Air Passenger Mile OR Emissions per Private Jet Flight Mile]

Single Flight

• Your Commercial Flight Emissions = Roundtrip Distance x Emissions per Commercial Air Passenger Mile x Number of Passengers
• Your Private Jet Flight Emissions = Roundtrip Distance x Emissions per Private Jet Flight Mile

Hotel Stay

• Hotel Emissions = Number of Guests x Number of Nights Stay x Emissions per Person per Hotel Night

Trip

• Your Trip Emissions = Flight Emissions + Hotel Emissions

Assumptions
Emissions per Commercial Air Passenger Mile = 0.00041 tons of CO₂
Emissions per Gallon of Gasoline = 0.0089 tons of CO₂
Emissions per Person per Hotel Night = 0.0136 tons of CO₂
Average Mid-Scale Hotel Size = 108 rooms
Average Mid-Scale Hotel Emissions = 370 tons of CO₂per year
Average Number of Guests per Car = 1
Average Fuel Economy = 22 mpg
Vegan Diet = 2.0 tons of CO₂
Vegetarian Diet = 2.7 tons of CO₂
Mostly Vegetarian Diet = 3.0 tons of CO₂
Omnivorous Diet = 3.8 tons of CO₂

• Your Event Emissions = Related Flight Emissions + Related Car Travel Emissions + Related Hotel Emissions + Related Diet Emissions
  
• Related Flight Emissions = Number of Your Guests Flying x Average Roundtrip Flight Distance x Emissions per Commercial Air Passenger Mile
  
• Related Car Travel Emissions = {[Number of Your Guests Driving x Average Roundtrip Distance of Their Drive] / Average Fuel Economy} x Emissions per Gallon of Gasoline
  
• Related Hotel Emissions = Number of Your Guests Staying in a Hotel x Number of Nights They Stay x Emissions per Person per Hotel Night
  
• Related Diet Emissions = {[Duration of Your Event x Average Yearly Emissions by Meal Type] / 365} x Number of Your Guests

Average Person: The United States was responsible for roughly 7.2 billion metric tons of CO₂ in 2005. Given a population of 294 million citizens at the time, and an approximate 1% emissions increase per year, that’s roughly 25 metric tons of CO₂ emissions per year per person. (Your individual emissions may vary markedly from this per capita average due to your location and your personal consumption choices.)

Average Household: According to the most recent U.S. Residential Energy Survey, the residential sector accounts for roughly 20% of U.S. energy-related CO₂ emissions, or an average of 5 tons CO₂ per person every year.

Average Driver: According to the U.S. Dept. of Energy’s Transportation Energy Data Handbook, the U.S. transportation sector accounts for roughly 33% of U.S. energy-related CO₂ emissions, with motor gasoline comprising 62%, or 5 tons per year of CO₂, and buses, trucks, ships and aircraft accounting for the remaining amount.

Our Sources

• Center for New American Dream’s
  http://www.newdream.org/turnthetide
• Department of Food and Rural Affairs, United Kingdom
  http://www.defra.gov.uk/
• U.S. Department of Energy’s Transportation Energy Data Handbook
  http://www-cta.ornl.gov/
• U.S. Energy Information Administration’s Residential Energy Consumption Survey
  http://www.eia.doe.gov/emeu/recs/contents.html
• U.S. Energy Information Administration’s Updated State-level Greenhouse Gas Emission Coefficients for Electricity Generation
  http://tonto.eia.doe.gov/FTPROOT/environment/e-supdoc-u.pdf#search=%22co2%20emissions%20electricity%20state%22
• U.S. Environmental Protection Agency
  http://www.epa.gov
• U.S. Environment Protection Agency, Fuel Economy Guide Report Files
  http://www.epa.gov/otaq/fereport.htm