Frequently Asked Questions
What do my calculator results mean?
Your personal carbon footprint is the sum of the information you input
into the calculator, resulting in an estimate of the carbon dioxide
that is produced by home energy use, transportation, and household waste.
The result is compared against an estimated annual per capita U.S. average
of 16,008 pounds resulting from home energy, transportation and household
Here are the comparative results:
Pounds of CO2 emissions per year
Below 6000 lbs/yr
Much less than average
Between 6000 and 11,010 lbs/yr
Less than average
Between 11,010 and 21,010 lbs/yr
Between 21,010 and 26,005 lbs/yr
More than average
Above 26,005 lbs/yr
Much more than average
How did we do the math on the calculator?
The calculator for your personal footprint was based on several areas
of energy use that have the greatest impact on carbon dioxide emissions
for most individuals: home energy, personal tranportation, and waste.
Home Energy Use
Based on the type of heating source you input, we used the following
Electricity Emissions = (average monthly electric bill / price per
kWh) * electricity emission factor * months in a year
We assumed a national average US price per kWh = $0.1
We used an electrical emission factor (electricity/kWh) = 1.37 [Source:
Information Administration (EIA). Electric Power Annual 2005, Table
5.1 (October 2006)]
Natural Gas Emissions = (average monthly gas bill / price per thousand
cubic feet) natural gas emission factor * months in a year
We assumed a national average US price per thousand cubic feet = $13.83
[Source: Energy Information Administration (EIA): Natural Gas Annual]
An emission factor (natural gas/thousand cubic feet) = 120.61 was used.
[Source: U.S. EPA, Inventory of U.S. Greenhouse Gas Emissions and Sinks:
1990-2004, Annex 2,Table A30]
Fuel Oil Emissions = (average monthly fuel oil bill / price per gallon)
fuel oil emission factor * months in a year
A national average of $2.37 per gallon was used. [Source: Energy Information
Administration: US No. 2 Distillate Prices by Sales Type, Table 15.]
Our emission factor used was (fuel oil/gallon) = 22.28 [Source: U.S.
EPA, Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2006,
Annex 2, Table A30]
Vehicle Emissions = (number of miles driven per week * weeks
in a year) / average vehicle fuel efficiency * pounds of CO2 emitted
We used an emissions factor of 19.564 per gallon of gasoline [Source:
Information Administration Fuel and Energy Source Codes and Emissions
Air travel emissions per passenger mile are significantly affected
by the length of the flight because a high percentage of fuel use and
emissions occur on take-off. Therefore we ask for number of short, medium,
and long flights.
The calculator input is the number of each type of flight, defined
as each leg of a flight. For example: a round trip flight with one stop
each way has four legs. We began with values from the GHG Protocol Initiative,
a widely recognized international accounting tool for government and
business leaders to understand, quantify, and manage greenhouse gas
GHG Flight definitions:
short haul: less than 452km*1.6094 = 727.45 miles (1.6094 is the conversion
factor for kilometers to miles)
med haul: less than 1600km*1.6094 = 2575.04 miles
long haul: more than 1600km*1.6094 = 2575.04 miles
We then created "averages" for each flight definition. For
short haul, rather than average between 0 and 727; we assumed that few
would fly if the distance they need to travel can be driven in 4 hours
or less. So, 4 hrs. @ 55 mi/hr = 220 (low value) + 727.45 (high value)
= 947.45/2 = 473.7 for an average short haul flight.
For medium haul, we went with the assumptions from GHG Protocol Initiative
- less than 2575.04 miles, and averaged that with the 727.45 value of
the upper limit for short haul. 1651.25 miles is the result.
For long haul, we researched the 10 longest distance non-stops and
averaged that number to get the higher value for the range: 8,793 miles.
We then averaged again between 8,793 and the 2575.04 miles that represents
the low value for the long haul category to achieve an average for the
long haul of 5684.02 miles.
Different per passenger emissions factors are used for each flight
length, as follows:
Short flight: .64 lbs/mile = 0.2897 kg CO2 per mile*2.2046 (factor
for conversion from kilograms to pounds)
Medium flight: .44 lbs/mile = 0.2028 kg CO2 per mile*2.2046 (factor
for conversion from kilograms to pounds)
Long flight: .39 lbs/mile = 0.1770 kg CO2 per mile*2.2046 (factor for
conversion from kilograms to pounds)
The total number of miles for each type of flight is multiplied by
the emissions factor for that type of flight to get pounds of carbon
dioxide, which are then added together to get the total carbon footprint
from air travel.
Since we created average flight distances to simplify our calculator
tool, your actual flight emissions may be higher or lower. For business
reporting and emissions management we suggest tracking actual fuel use
and type of fuel use for flights - or exact mileage, if fuel use is
not available. GHG Protocol provides spreadsheets and instructions for
more precise reporting of mobile emissions.
Air travel definitions and per passenger emissions factors for each
are from the GHG
Protocol Mobile Combustion Tool.
Emissions factors for fuel used in the formula are from the EIA Coefficients
We based our estimate of the environmental impact of household waste
on data from the EPA, with 1010lbs. per person annually being the average.
This average was obtained by dividing the tons of waste deposited annually
at US landfills by US population.
Emissions = number of people in household * average lb CO2 equivalent.
generated from waste per person per year [Source: Based on EPA's Inventory
of U.S. Greenhouse Gas Emissions and Sinks 1990-2004, Chapter 8, Table
How Was the Reduction Calculated?
Replacing incandescent light bulbs with compact fluorescents: assumes
that lights are on for 4 hours per day.
Replacing old refrigerator with an ENERGY STAR® model: assumes
old model uses 820 kWh per year; ENERGY STAR model uses 440 kWh per
Turning up thermostat for central air conditioner: assumes average
household electricity use of approximately 940 kWh per month, and that
air conditioners account for about 7 percent of residential electricity consumption.
EIA 2009. Residential Energy Consumption]
Turning down thermostat in winter: assumes 1 percent savings in energy
use for a 1 degree decrease. assumes thermostat is turned down for 8
hours each night November through March.
Replacing single-glazed windows with ENERGY STAR windows: Assumes 2000
square-foot house, 300 square feet of glass, gas heat, and electric
Replacing an old boiler or furnace with an ENERGY STAR model: Assumes
a 20 percent savings on heating fuel costs.
Except where noted above, all home emissions reductions were based on
data from: ENERGY
Emissions reductions were calculated using the same formulas shown
above, and the resulting amount was subtracted from your previous total
For our estimated reduction in greenhouse gas emissions that you can
achieve by recycling, we used emissions data for each source: newspaper,
glass, plastic, and metal. Our reduction calculations assume that households
recycle 100 percent of all recyclable materials generated as waste.
The plastic material type used in the calculator includes PET and HDPE,
and the metal material type includes aluminum and steel cans.
[Emissions Factors Source: U.S. Environmental Protection Agency, 2006.
Solid Waste Management and Greenhouse Gases: A Life-Cycle Assessment
of Emissions and Sinks, EPA530-R-06-004.]
FInd energy data from the US Energy Information Administration online
Environmental information can be found online at: http://www.epa.gov/
Find energy data for home and transportation fuel use online at: http://www.eia.doe.gov/oiaf/1605/coefficients.html
Want to know more about carbon footprints? Visit the Wikipedia page: