How this calculator works
The trip distance is doubled for a return journey and divided by fuel economy to get the fuel used. Multiplying by the pump price gives the total cost, which is split equally between the people in the car. Carbon dioxide is estimated from the litres burned using a fixed combustion factor for gasoline or diesel. The page assumes that everyone shares the same journey and that the car would make the trip anyway; it does not account for detours to collect passengers, idling in traffic or the extra weight of a full car.
Formula
litres = total distance (km) / fuel economy (km/L). Total fuel cost = litres x price per litre. Cost per person = total cost / people. CO2 = litres x 2.289 kg/L for gasoline or 2.663 kg/L for diesel.
Worked example
A 40 km one-way commute driven both ways at 8 L/100 km uses 6.4 L. At $1.65 a litre the trip costs $10.56, or $3.52 each when three people share. Gasoline produces about 14.65 kg of carbon dioxide, or 4.88 kg per person, so each rider avoids about 9.77 kg compared with driving alone.
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Frequently asked questions
Should the driver pay the same share as passengers?
This page splits the fuel cost equally. Many carpools treat the cost differently, for example letting the driver keep the vehicle for errands or charging a flat rate. Enter the number of people sharing the cost rather than the number of seats.
Does carpooling really reduce emissions?
Sharing one car reduces emissions per person when the alternative is several cars making the same trip. The total fuel burned by the shared car is still the same, and a detour or a heavier load can increase it slightly.
Which fuel economy figure should I use?
Use the average you actually achieve over a full tank, not the best highway rating. City driving, winter conditions and air conditioning can raise consumption well above the published combined figure.
Can I mix gasoline and diesel passengers?
No. The car burns one fuel. Choose the fuel type of the vehicle, because the carbon dioxide factors are different.