The fuel cost formula
Fuel cost = distance ÷ fuel economy × fuel price. In the US, with miles per gallon: a 600-mile round trip in a car that gets 30 mpg uses 20 gallons; at $3.20 a gallon that's $64. In metric, with liters per 100 km: 800 km at 7 L/100 km uses 56 liters. Our fuel cost calculator works out both.
Holiday travel season
Thanksgiving and the December holidays are the busiest road-travel periods of the year in the US. Fuel prices can change before these weekends, so check local prices a few days before you leave and fill up away from highway service stations, which are often more expensive.
Real-world fuel economy
The official rating is a best case. Highway speeds above 60–65 mph, heavy loads, roof boxes, cold weather and under-inflated tires all reduce efficiency. Plan with 10 to 15% worse economy than the sticker figure to avoid surprises.
Converting MPG and L/100 km
To convert, divide 235.2 by the value: 30 mpg (US) ≈ 7.8 L/100 km, and 6 L/100 km ≈ 39 mpg. Our km to miles converter also helps when planning international routes.
Splitting costs
Divide total fuel cost by the number of passengers for a fair share. Add tolls and parking if you want to split the full travel cost. Carpooling is one of the easiest ways to cut the cost per person.
Habits that save fuel
Smooth acceleration and braking, using cruise control on highways, removing unnecessary weight and keeping tires at the recommended pressure can together save up to 15 to 20%. Driving at 65 mph instead of 75 mph uses noticeably less fuel on long trips.
Electric vehicles
For EVs, multiply distance by energy use (kWh per mile or per 100 km) and by your charging price. Public fast chargers usually cost more per kWh than charging at home; our electricity cost calculator can estimate home charging.
Plan the budget
Add fuel, food, accommodation and a 10% buffer. Knowing the number in advance makes the trip more relaxing.
Frequently asked questions
How do I calculate gas cost for a trip?
Distance ÷ miles per gallon × price per gallon.
How much gas does a 600-mile trip use?
About 20 gallons in a car that gets 30 mpg.
How do I convert mpg to L/100 km?
Divide 235.2 by the mpg value.
What is the best speed for fuel economy?
Most cars are most efficient around 50–60 mph; economy drops at higher speeds.