Sharing a car to work or school splits fuel, parking and tolls and takes cars off the road. Even two people sharing halves the cost and the emissions per person, and many cities offer carpool lanes and cheaper parking for shared cars.
How to use the Carpooling Calculator
- One-way distance
- Round trip
- Trips per month
- Fuel economy given as
- Fuel economy
- Fuel consumption
- Fuel price
- Parking and tolls per trip
- People sharing the car
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter the one-way distance, whether you drive both ways, the trips per month, fuel economy, fuel price, parking and tolls, and how many people share. The calculator splits the costs and compares them with driving alone.
Tips
- Use your own measured figures – fuel economy, speed and prices vary a lot with driving style, traffic, load and season.
- Pick the unit in each field’s menu (miles or kilometres, mpg or L/100 km); the calculator converts everything for you.
- Fill up to the brim twice and divide the distance by the fuel added to measure real fuel economy.
- For vehicle modifications, treat results as a starting point and confirm with the parts maker or a professional mechanic.
Common mistakes to avoid
- Mixing US and imperial (UK) gallons – a UK gallon is about 20% bigger.
- Using the advertised fuel economy instead of real-world figures.
- Forgetting tolls, parking and wear and tear when comparing driving with public transport.
Inputs explained
| Field | What to enter |
|---|---|
| One-way distance | Units: mi, km, m, nmi |
| Round trip | Choose one: No, Yes |
| Trips per month | A number |
| Fuel economy given as | Choose one: Distance per volume (mpg, km/L), Litres per 100 km |
| Fuel economy | Units: mpg (US), mpg (UK), km/L |
| Fuel consumption | In L/100 km |
| Fuel price | Units: /US gal, /L, /UK gal |
| Parking and tolls per trip | Amount in your currency |
| People sharing the car | A number |
What each result means
- Trip cost (fuel + parking) = [Fuel per trip]×[Fuel price] + [Parking and tolls per trip]
- Cost per person per trip = [Trip cost (fuel + parking)]÷[People sharing the car]
- Monthly saving per person = ([Trip cost (fuel + parking)] – [Trip cost (fuel + parking)]÷[People sharing the car])×[Trips per month]
- CO₂ saved per month (petrol) = [Fuel per trip]×2347.697029306865×[Trips per month]×([People sharing the car] – 1)
Example values
How the main result changes when One-way distance changes and everything else stays at the example values above:
| One-way distance (mi) | Cost per person per trip |
|---|---|
| 7.5 | 2.37 |
| 11.25 | 2.72 |
| 15 | 3.07 |
| 18.75 | 3.42 |
| 22.5 | 3.77 |
| 30 | 4.47 |
Formula
Fuel per trip = distance × (2 if round trip) ÷ fuel economyCost per person = fuel cost ÷ peopleMonthly saving per person = (solo cost − shared cost) × trips per monthWorked example
Inputs — One-way distance: 15 mi; Round trip: Yes; Trips per month: 22; Fuel economy given as: Distance per volume (mpg, km/L); Fuel economy: 25 mpg (US); Fuel consumption: 8 L/100 km; Fuel price: $3.5 /US gal; Parking and tolls per trip: $5; People sharing the car: 3.
Results — Fuel per trip = 1.2 US gal; Trip cost (fuel + parking) = $9.20; Cost per person per trip = $3.07; Monthly saving per person = $134.93; CO₂ saved per month (petrol) = 469.2 kg.
Frequently asked questions
How much can I save by carpooling?
With three people sharing, each pays a third of the fuel, parking and tolls – often $100+ a month on a typical commute.
How do I split carpool costs fairly?
Share fuel, parking and tolls equally; some groups also add a per-mile allowance to the driver for wear and tear.
How much CO₂ does carpooling save?
Each car left at home avoids about 8.9 kg of CO₂ per US gallon of petrol not burned.
What formula does the Carpooling Calculator use?
Fuel per trip = distance × (2 if round trip) ÷ fuel economy.