How to Work Out the Fuel Cost of a Road Trip
Estimate what a road trip will cost in fuel from the distance, your car's fuel economy and the pump price, in miles per gallon or liters per 100 km.
By the CalClu team2 min read
Fuel is usually the biggest variable cost of a road trip, and it's easy to estimate before you leave. You need three numbers: the distance, how much fuel your car uses and the fuel price.
In miles and gallons
A 420-mile trip in a car that averages 30 MPG uses 14 gallons. At $3.50 a gallon, that's $49.00 each way.
In kilometers and liters
Much of the world measures economy in liters per 100 km (L/100 km), where a lower number is better:
A 650 km trip at 6.5 L/100 km uses 42.25 liters. At €1.80 a liter, that's about €76.
Find your real fuel economy
The official figure is often optimistic. To measure your own, fill the tank, reset the trip meter, drive as usual, then fill up again.
To convert, divide 235.2 by US MPG to get L/100 km, and the same formula works the other way. 30 MPG is about 7.8 L/100 km.
What changes the number
- Highway speed: air resistance rises sharply with speed, so 75 mph uses noticeably more fuel than 65 mph.
- Load and roof boxes: extra weight and drag both cost fuel.
- Air conditioning, idling and stop-start traffic all add up.
Add 10–15% as a buffer if you'll be driving through mountains, in heavy traffic or with a full car.
Planning the drive
Distance ÷ average speed gives your driving time. Remember that average speed over a long trip, including slow sections, is usually well below the speed limit, and plan breaks every couple of hours.
Splitting the cost
Divide the total fuel cost by the number of travelers. Include tolls and parking if you're splitting the whole trip.
Try the calculators
More tools in this area: Automotive & Travel calculators