Calculate your home energy, auto, and food emissions to answer the question, “What’s my carbon footprint?” — compared to the average in the United States.
I took an environmental studies class that used this carbon-footprint formula, and I thought I’d share with everyone. It’s a way for roughly calculating household carbon footprint and thinking about things you can do to reduce your personal emissions. If nothing else, I think it’s great that schools are encouraging students to at least think about areas in our lives that contribute to carbon emissions and ways we can adopt more sustainable, conservative practices to mitigate some of the effects of energy-related pollution.
The Facts
- About 80 percent of human contributions to global warming comes from carbon dioxide emissions; mostly from burning fossil fuels.
- Worldwide, each person emits an average of 4.5 ton carbon dioxide each year — but this average is immensely skewed upward by those in the United States and other rich nations.
Calculating Household Carbon Footprint
If math isn’t your thing, try the online carbon calculators provided by the following organizations: EPA or the Berkeley Cool Climate Calculator. However, these tools are built on formulas, likely in line with the equations below. It’s important to know what will go into these calculations even when using a tool.
Transportation Emissions
Estimate the average miles you drive each year and your car’s average miles per gallon. The worksheet says to use 20 mpg if you’re not sure, but dividing the number of miles shown on your gauge when it’s about empty by the total number of gallons in your fuel tank should get your pretty close. (For example, I know I need to fill up my Ford Focus when I get around 280 miles for my 12-gallon tank, so my car’s mpg is about 23).
Here’s the formula:
Average miles/year x Average mpg = Gallons/year
Burning 1 gallon of gas emits 9 kg of carbon dioxide into the atmosphere. So to calculate your driving emissions:
Gallons/year x 9 kg/gallon = Kilograms of Carbon dioxide/year
Electricity Emissions
Estimate the amount of kilowatt-hours you consume each year. You can do this by either looking at your most recent electric bill and multiplying the amount of kilowatt hours you were charged for by 12 — or go with the typical amount consumed by a U.S. household of 3,000 kWh per year.
One kilowatt-hour of electricity produced from a coal-fired plant is equivalent to 1 kg of carbon dioxide emitted into the air. So your average kilowatt-hours of electricity per year is equal to the kilograms of carbon dioxide emitted for its production.
See our Electricity Quiz to find out more about electricity consumption and emissions.
Natural Gas Emissions
Estimate the average amount of energy you use each year to heat your homes (often expressed in British Thermal Units, or BTUs). The worksheet gave 60 million BTUs per year as the typical amount for a U.S. household if you don’t know yours. However, just as calculating the electricity emissions, find your last heating bill and multiply the units by 12 to get your yearly consumption.
100,000 BTUs is equivalent to 5.5 kg of carbon dioxide. Here’s the formula:
BTUs-per-year ÷ 100,000 BTU x 5.5 kg = Average natural gas emissions/year
Travel Emissions (Flying)
Estimate the number of miles you traveled by airplane last year. On average, one mile traveled by plane equals 0.23 kg of carbon dioxide emissions, so:
Number of miles of airplane travel x 0.23 kg = Airplane travel emissions
For more information about travel emissions, see Tips for Eco-Friendly Travel.
What’s My Carbon Footprint?
Add the carbon dioxide totals highlighted in bold.
Car emissions + Electricity emissions + Natural gas emissions + Airplane travel emissions
Food Emissions
Multiple the carbon dioxide totals calculated about by 2. The worksheet said the carbon dioxide we emit indirectly through purchasing food and other goods and services is twice the amount we emit in the ways calculated above.
Total from above x 2 = Total carbon dioxide emissions (in kg/year)
A Note on Conversions
When doing carbon calculations, you often need to convert kilograms per year to metric tons per year. Here’s how:
Total carbon dioxide emissions ÷ 1,000 metric tons/year = Metric tons/year of carbon dioxide emissions
Then the worksheet tells us to compare this number with the average per capita carbon dioxide emissions globally and nationally.
Is your total carbon dioxide emission greater than 1 ton per year? Is it greater or less than 20 tons per year? Where do most of your emissions come from? How could you lower this amount?
I’d never calculated my emissions total before, but now knowing mine as it currently stands (a number the author cares not to share out of embarrassment) has really made me see where I need to make improvements and how much carbon dioxide I alone contribute to the global total. Before calculating my carbon footprint, I think I applied the term “emissions” nationally, presuming my carbon feet couldn’t possibly have as large a print on the nation’s total. But with my number being so … unsatisfactory … it puts the term, and the problem, into a perspective I can relate to.
