Carpool Savings Calculator
What sharing a commute saves each person in fuel money, and what it saves the road and the air in kilometres driven and CO₂ — for two, three or four people taking turns.
If n people share one car instead of driving n cars, the group drives one car’s worth of kilometres instead of n.
How the carpool savings calculator works
If n people share one car instead of driving n cars, the group drives one car’s worth of kilometres instead of n. Each person’s share of the fuel falls to 1 ÷ n of what they paid alone. The calculator uses the car’s fuel consumption, the fuel price and 2.31 kg of CO₂ per litre of petrol (2.68 for diesel) to turn the kilometres removed into money and emissions.
Formula: per-person saving = solo fuel cost × (1 − 1 ÷ n); CO₂ avoided = km removed × L/100 km ÷ 100 × kg CO₂ per litre
Worked examples
| Inputs | Fuel saved per person per year | Note |
|---|---|---|
| 20 km each way, two sharing, 8 L/100 km at 2.00 | 736 | 736 each per year |
| Four sharing | 1,104 | 1,104 each |
| Diesel, 35 km, three sharing, 3 days a week | 606.97 | 607 each |
FAQFrequently asked questions
Does taking turns or paying the driver change the maths?
Not the total: whether you alternate cars or one drives and others chip in, the group burns one car’s fuel. Alternating also spreads the wear and the parking.
What about tolls, parking and wear?
They add to the saving — parking in particular is often more than the fuel. Add them to the fuel price per kilometre if you want them in the figure: divide your yearly parking by the yearly kilometres.
Is a carpool better than the bus?
Two people in a typical car emit about the same per person as a bus; three or four beat it. A full car on a direct route is one of the lowest-emission ways to commute short of rail or a bicycle.
What does the CO₂ figure include?
Only the fuel burned — the tailpipe figure most conversion tables quote. Including fuel production adds about 20%.
Where these figures come from
- UK DESNZ / DEFRA — Greenhouse gas reporting: conversion factors — the flight, fuel and waste emission factors used here
- Scarborough et al. (2014), Climatic Change — Dietary greenhouse gas emissions — the per-diet daily emission figures
- US EPA — Technical Assistance Document for the Reporting of Daily Air Quality (AQI) — the PM2.5 breakpoints the air quality calculator uses
- Australian Government — National Greenhouse Accounts Factors — the official Australian emission factors
Last checked: September 2026. Factors are taken from published government and peer-reviewed sources, each named on the page with its year.