Commute Emissions Calculator

For gasoline and hybrid vehicles, both CO2 per mile and fuel cost per mile are calculated by dividing a fixed per-gallon figure (emissions or price) by your entered MPG, so raising MPG lowers both quantities proportionally from the same underlying calculation. A car that gets twice the fuel economy of another, driven the same annual mileage, produces roughly half the annual emissions and roughly half the annual fuel cost in this model.

No -- electric vehicles, bus/transit, and bike/walk all use fixed per-mile emissions and cost rates in this calculator that do not reference the MPG field at all. MPG only affects the result when Vehicle Type is set to Gasoline Car or Hybrid, since those are the two vehicle types whose per-mile emissions and fuel cost are calculated from fuel economy.

It's built from the EPA's eGRID database, which reports the U.S. national average CO2 emissions intensity of the electric grid (roughly three-quarters of a pound of CO2 per kWh generated, nationally averaged, and updated periodically as the grid's generation mix shifts), combined with typical EV energy consumption per mile. Because it uses a single national average rather than your specific utility's grid mix, an EV commute charged from a coal-heavy regional grid will actually produce more emissions than this figure suggests, while one charged from a grid with more hydro, nuclear, wind, or solar will produce less.

The trees-to-offset estimate divides your total annual CO2 emissions in pounds by the EPA's estimate of roughly 132 pounds (60 kg) of CO2 absorbed per year by a medium-growth urban tree over its first 10 years, then rounds up to a whole number of trees. Real carbon absorption varies significantly by tree species, age, and growing conditions, so this is a rough illustrative comparison rather than a precise offset calculation.

Annual miles is calculated as one-way distance times two (for the round trip) times days per week times 52 weeks, so distance and days per week enter that formula the same way -- as direct multiplicative factors. Increasing either one by 20%, holding the other fixed, raises annual miles by 20%, which in turn raises annual CO2 emissions by the same 20% for any given vehicle type and fuel economy.