Carbon Footprint Calculator Formula

Understand the math behind the carbon footprint calculator. Each variable explained with a worked example.

Use the Carbon Footprint Calculator

Formulas Used

Total Annual CO2

total_co2 = elec_co2 + gas_co2 + drive_co2

Electricity CO2

electricity_share = elec_co2

Natural Gas CO2

gas_share = gas_co2

Driving CO2

driving_share = drive_co2

Variables

VariableDescriptionDefault
electricity_kwhMonthly Electricity Use(kWh)900
gas_thermsMonthly Natural Gas Use(therms)50
miles_drivenAnnual Miles Driven(miles)12000
car_mpgVehicle Fuel Economy(mpg)25
elec_co2Derived value= electricity_kwh * 12 * 0.92 / 2204.6calculated
gas_co2Derived value= gas_therms * 12 * 11.7 / 2204.6calculated
drive_co2Derived value= (miles_driven / car_mpg) * 19.6 / 2204.6calculated

How It Works

How to Calculate Your Carbon Footprint

Your carbon footprint is the total greenhouse gas emissions from your activities, measured in metric tons of CO2 per year.

Key Emission Factors

  • Electricity: ~0.92 lbs CO2 per kWh (US average grid mix)
  • Natural Gas: ~11.7 lbs CO2 per therm burned
  • Gasoline: ~19.6 lbs CO2 per gallon combusted

    • Formula

    Total CO2 (metric tons) = (Electricity CO2 + Gas CO2 + Driving CO2) / 2204.6

    Each source is computed from usage multiplied by its emission factor, then converted from pounds to metric tons.

    Worked Example

    A household uses 900 kWh of electricity per month, 50 therms of gas per month, and drives 12,000 miles per year in a 25 mpg vehicle.

    electricity_kwh = 900gas_therms = 50miles_driven = 12000car_mpg = 25
    1. 01Electricity CO2: 900 * 12 * 0.92 = 9,936 lbs = 4.51 metric tons
    2. 02Natural Gas CO2: 50 * 12 * 11.7 = 7,020 lbs = 3.18 metric tons
    3. 03Driving CO2: (12000 / 25) * 19.6 = 9,408 lbs = 4.27 metric tons
    4. 04Total: 4.51 + 3.18 + 4.27 = 11.96 metric tons CO2/year

    Frequently Asked Questions

    What is a carbon footprint?

    A carbon footprint is the total amount of greenhouse gases your activities produce, expressed as CO2 equivalents. The average American generates about 16 metric tons per year.

    How can I reduce my carbon footprint?

    The most impactful steps are switching to renewable electricity, improving home insulation, driving less or switching to an EV, and reducing air travel.

    Why is it measured in metric tons?

    Metric tons (1,000 kg or ~2,204.6 lbs) provide a standard international unit that makes it easy to compare emissions across countries and sectors.

    Ready to run the numbers?

    Open Carbon Footprint Calculator