Car — gas / diesel
Emissions = miles × (CO₂ per gallon ÷ MPG). CO₂ per gallon: gasoline 8.89 kg, diesel 10.18 kg, hybrid 8.89 kg.
| Car type | Fuel | MPG used |
|---|
| Small car | Gasoline | 35 MPG |
| Medium car | Gasoline | 28 MPG |
| Large car | Gasoline | 22 MPG |
| SUV | Gasoline | 18 MPG |
| Small car | Diesel | 40 MPG |
| Medium car | Diesel | 32 MPG |
| Large car | Diesel | 26 MPG |
| SUV | Diesel | 22 MPG |
| Hybrid | Gasoline | 50 MPG |
Tailpipe emissions only. Source: US EPA fuel economy data.
Electric vehicle
Emissions = miles × efficiency (kWh/mi) × grid emission factor. Default: 0.30 kWh/mi (US average). Clean energy charging sets factor to 0. State grid uses the factor from the electricity section.
Flights
Great-circle distance with 9% routing uplift. Includes Radiative Forcing Index (RFI) multiplier of 1.9× for non-CO₂ effects at altitude. Per-km factors: short-haul <800 km — 0.255 kg CO₂e/km; medium 800–3,700 km — 0.195 kg CO₂e/km; long-haul >3,700 km — 0.148 kg CO₂e/km. Class multipliers: economy 1×, business 2×, first 4×.
Public transport
| Mode | Factor | Source |
|---|
| Train / subway | 0.041 kg CO₂e/km | EPA / DEFRA 2023 |
| Bus | 0.105 kg CO₂e/km | EPA average |
Home heating
| Fuel | Factor | Unit |
|---|
| Natural gas | 5.3 kg CO₂e | per therm |
| Heating oil | 10.21 kg CO₂e | per gallon |
| Propane | 5.74 kg CO₂e | per gallon |
| Heat pump / electric | 0 | (counted in electricity) |
| Wood / biomass | 0 | (assumed carbon-neutral) |
Source: US EIA combustion emission factors.
Electricity grid factors (kg CO₂e per kWh)
State-level factors from US EPA eGRID 2022. US average: 0.386. Notable: Vermont 0.011, Washington 0.095, California 0.200, Texas 0.421, West Virginia 0.737. Clean energy checkbox sets factor to 0.
Comparison benchmarks
| Benchmark | Value |
|---|
| US average per person | ~16 t CO₂e/yr |
| Global average per person | ~4.7 t CO₂e/yr |
| Paris Agreement target (2050) | ~2 t CO₂e/yr |
All figures are estimates. Sources: US EPA eGRID 2022, EIA combustion factors, DEFRA 2023 GHG conversion factors, IPCC AR6.