Quick answer: Fuel needed = distance × liters per 100 km ÷ 100, and cost = fuel needed × price per liter. A 500 km trip at 7 L/100 km needs 35 liters, and at $1.50 a liter that is $52.50, or $105 for the round trip. Fuel economy in miles per gallon converts as L/100 km = 235.215 ÷ MPG (US).
Before a road trip, a commute to a new job or a car-sharing arrangement, it helps to know what the fuel will cost. Fuel economy is quoted in different ways around the world: liters per 100 km in Europe, miles per gallon in the US and UK, and kilometers per liter in much of Asia. This calculator accepts all of them.
Enter the distance, your car’s fuel economy and the fuel price. It shows how much fuel you need, the cost of the trip, the cost per kilometer or mile, and each person’s share if the cost is split.
How the cost is worked out
Cost = liters needed × price per liter
Cost per person = cost ÷ number of people
Other fuel economy units are converted to liters per 100 km first: km/L → 100 ÷ km/L, US MPG → 235.215 ÷ MPG, and UK MPG → 282.481 ÷ MPG. UK gallons are bigger than US gallons (4.546 liters against 3.785), which is why UK MPG figures look higher for the same car.
This estimates fuel only. Real fuel use depends on speed, traffic, load, air conditioning, tire pressure and driving style, and can be 10 to 30% more than the manufacturer’s figure. Tolls, parking and wear on the car are extra. For a safer budget, use your actual fuel economy from recent tanks.
A worked example
Example. A 500 km trip in a car that uses 7 L/100 km needs 500 × 7 ÷ 100 = 35 liters. At $1.50 a liter, that is $52.50. Tick “round trip” and it doubles to 70 liters and $105.00. Split between three people, each pays $35.00. In US units, 300 miles at 30 MPG with fuel at $3.50 a gallon needs 10 gallons and costs $35.00.
Fuel economy in four units
| L/100 km | MPG (US) | MPG (UK) | km per liter |
|---|---|---|---|
| 4 | 58.8 | 70.6 | 25.0 |
| 5 | 47.0 | 56.5 | 20.0 |
| 6 | 39.2 | 47.1 | 16.7 |
| 7 | 33.6 | 40.4 | 14.3 |
| 8 | 29.4 | 35.3 | 12.5 |
| 10 | 23.5 | 28.2 | 10.0 |
| 12 | 19.6 | 23.5 | 8.3 |
A lower L/100 km means a more efficient car, while a higher MPG or km per liter means the same.
Common mistakes to avoid
- Using the car’s brochure figure. Real fuel use is often 10 to 30% higher, so use your own average from recent tanks.
- Mixing US and UK gallons. A UK gallon is about 20% bigger, so the same car has a higher MPG figure in the UK.
- Forgetting other trip costs. Tolls, parking and wear on the vehicle are not included in the fuel cost.
Frequently asked questions
How do I calculate the fuel cost of a trip?
Divide the distance by your fuel economy to get the fuel needed, then multiply by the price per unit of fuel. For 500 km at 7 L/100 km, fuel is 35 liters, and at $1.50 a liter the cost is $52.50.
How do I find my car’s fuel economy?
Check the manual, or fill the tank, reset the trip meter, drive normally, refill and divide the distance by the fuel added. Repeat a few times for a good average.
How do I convert MPG to L/100 km?
Divide 235.215 by the MPG (US). 30 MPG is about 7.8 L/100 km. For UK MPG, divide 282.481 by the figure. This calculator does the conversion for you.
Is the price per liter or per gallon?
Choose the unit shown on the fuel pump. Most countries price per liter. The US prices per US gallon. The tool converts either one.
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Sources and further reading
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