How to calculate your carbon footprint

You need three things: your utility bills, a rough idea of how far you drive and fly, and an honest look at what you eat. This guide shows the math and a worked example.

Open the tool: Carbon Footprint Calculator

Step 1: Home energy

Add up a year of electricity in kWh and multiply by your grid factor, 0.38 kg per kWh for the US average. Add natural gas in therms times 5.4 kg. Divide the total by the number of people in the household.

Example: 10,500 kWh and 550 therms for two people is (4,030 + 2,950) ÷ 2 = 3.5 tons each.

Step 2: Driving

Divide miles driven by miles per gallon to get gallons, then multiply by 8.7 kg for gasoline. 11,000 miles at 26 mpg is 423 gallons, or 3.7 tons.

Step 3: Flights

Estimate the miles flown and multiply by about 0.2 kg per passenger-mile in economy with the contrail effect. A return trip from Chicago to Cancun, around 2,900 miles, comes to roughly 0.6 tons.

Step 4: Food

An average meat eater's diet is about 2.1 tons a year, a vegetarian diet about 1.4 and a vegan diet about 1.1. Beef and lamb make most of the difference.

Putting it together

Our example person totals about 3.5 + 3.7 + 0.6 + 2.1 = 10 tons, below the US average of 14 but four times the 2030 target. The biggest levers are heating and the car, which is typical for American households.