How to use it
- Choose your Units: metric for litres and km, or US or UK for gallons and miles.
- Pick What to calculate. For a trip, enter the Distance one way, the Fuel consumption and the Fuel price.
- Enter the Number of people sharing the cost, and tick Round trip if you drive back the same day.
- Read the Total fuel cost and the Cost per person. For your real consumption, switch to Consumption from a fill-up.
How the fuel cost is calculated
The calculator works out how much fuel the trip needs and then multiplies it by the price. The fuel needed is the total distance times the consumption, divided by 100 when the consumption is in litres per 100 km.
Fuel (litres) = distance (km) × consumption (L/100 km) ÷ 100
Cost = fuel × price per litre
Cost per person = cost ÷ number of people
Cost per km = cost ÷ distance (km)- With round trip ticked, the distance is doubled before this step.
- In US and UK units the fuel is counted in gallons, so the price is per gallon.
Converting L/100 km and mpg
Europe quotes fuel use in litres per 100 km; the US and UK quote miles per gallon. The two are linked by a constant: mpg = 235.215 ÷ (L/100 km) for the US gallon, and mpg = 282.481 ÷ (L/100 km) for the UK gallon.
The UK gallon is larger than the US gallon, so the same car shows a higher mpg in the UK. A car at 6.5 L/100 km gives 36.2 mpg (US) or 43.5 mpg (UK).
What this calculator does not include
- Parking, tolls, ferry fares and the wear on the car.
- Changes in consumption from speed, traffic, a roof box or a heavy load. A fill-up over a mixed journey is more reliable than one short trip.
- Discounts, loyalty points and price changes during the trip.
Worked example: 300 km each way at 6.5 L/100 km, 1.60 a litre, two people
The trip is 300 km there and 300 km back, so 600 km in total. At 6.5 L/100 km it needs 600 × 6.5 ÷ 100 = 39.0 litres.
At 1.60 a litre the fuel costs 39.0 × 1.60 = 62.40. Shared by two people that is 31.20 each, and 62.40 ÷ 600 km = 0.104 per km.
| Result | |
|---|---|
| Fuel needed | 39.0 L |
| Total fuel cost | 62.40 |
| Cost per person | 31.20 |
| Cost per km | 0.104 |
Frequently asked questions
How many litres does a 300 km trip use?
At 6.5 litres per 100 km, a 300 km trip uses 19.5 litres, and a round trip of 600 km uses 39.0 litres. Enter your own consumption to get your figure.
What is the difference between L/100 km and mpg?
L/100 km is the number of litres used for 100 km, so a lower figure is more economical. Miles per gallon is the number of miles driven per gallon, so a higher figure is more economical. The calculator converts one into the other.
Why does the UK show a higher mpg than the US?
The UK (imperial) gallon is 4.546 litres and the US gallon is 3.785 litres. The same car uses the same fuel, so its mpg is about 20 percent higher in the UK.
How do I measure my real fuel consumption?
Fill the tank to the top, note the trip meter, drive normally, fill to the top again and divide the distance by the fuel added. The fill-up option of this calculator does that calculation for you.
Does the cost include the return trip?
Only when you tick round trip. Without it the calculator uses the one-way distance you typed; with it the distance is doubled before the fuel is worked out.
Does the calculator keep the numbers I type?
No. The calculation runs in your browser, and nothing you type is sent to a server or saved for later.
Sources
Figures and text last checked on Tuesday, November 10, 2026.