Overview
A personal carbon footprint is the total greenhouse gas emissions caused directly and indirectly by an individual in a year, measured in metric tons of CO₂-equivalent (MT CO₂e). The calculator covers four main categories: transportation, home energy, diet, and flights.
US context: The average American produces about 16 MT CO₂e per year (EPA 2023). The global average is roughly 4 MT per year (IPCC AR6 SPM). Reducing personal emissions toward 2–4 MT/year is a rough goal consistent with Paris Agreement warming limits.
Emission Factors
The calculator uses US-EPA emission factors (2022–2023 vintage):
| Source | Factor |
|---|---|
| Gasoline | 8.887 kg CO₂e / gallon |
| US electricity grid | 0.386 kg CO₂e / kWh |
| Natural gas | 5.3 kg CO₂e / therm |
| Short-haul flight (round trip) | 0.255 MT CO₂e |
| Long-haul flight (round trip) | 1.620 MT CO₂e |
Diet estimates are based on lifecycle analysis from EPA/USDA data:
| Diet type | MT CO₂e / year |
|---|---|
| Meat-heavy | 3.3 |
| Average | 2.5 |
| Vegetarian | 1.7 |
| Vegan | 1.5 |
Formulas by Category
Transportation (driving):
gallons/year = milesPerYear / mpg
transportMT = gallons/year × 8.887 / 1000Home electricity:
electricityMT = kWhPerMonth × 12 × 0.386 / 1000Natural gas:
naturalGasMT = thermsPerMonth × 12 × 5.3 / 1000Flights:
flightsMT = shortFlights × 0.255 + longFlights × 1.620Total:
totalMT = transportMT + electricityMT + naturalGasMT + dietMT + flightsMTWorked Example
Consider the US-average household driver:
- 12,000 miles/year at 28 MPG
- 877 kWh/month electricity (US EIA 2022 average)
- 50 therms/month natural gas
- Average diet (2.5 MT/year)
- 2 short-haul flights/year, no long-haul
Transportation: 12,000 ÷ 28 = 428.6 gallons × 8.887 / 1,000 = 3.81 MT
Electricity: 877 × 12 × 0.386 / 1,000 = 4.06 MT
Natural gas: 50 × 12 × 5.3 / 1,000 = 3.18 MT
Diet: 2.50 MT
Flights: 2 × 0.255 = 0.51 MT
Total: 14.06 MT CO₂e — about 12% below the US average of 16 MT.
Biggest Levers for Reduction
Most people’s footprints are dominated by 2–3 categories. The largest categories in the worked example above, in order, are:
- Electricity (4.06 MT) — switching to renewable electricity or improving efficiency has a large impact
- Transportation (3.81 MT) — reducing miles driven, carpooling, or transitioning to an EV
- Natural gas (3.18 MT) — home heating and water heating; electrification has high leverage
- Diet (2.50 MT) — shifting toward vegetarian or vegan diet reduces this by 30–55%
- Flights (0.51 MT) — a single long-haul round trip adds 1.62 MT
Limitations of Personal Carbon Footprint Estimates
Scope 3 emissions are excluded. The calculator covers direct and near-direct emissions (scope 1 and 2). It does not include the embodied carbon of manufactured goods you purchase, the upstream emissions of the food supply chain (beyond diet category averages), or financial investments.
Grid averages vary by location. The 0.386 kg CO₂e/kWh factor is the US average. If you live in a region with high renewable penetration (Pacific Northwest hydro, for example), your actual electricity emissions may be 50–80% lower. If you live in a coal-heavy region, they may be higher.
Individual variation. The diet factors are national averages, not individualized. They represent the approximate lifecycle footprint of each diet pattern, not a precise measurement of your specific food choices.