How to use it
- Pick your efficiency unit. Choose km per litre, litres per 100 km or miles per gallon — whatever your car’s trip computer or handbook shows. The distance and price fields relabel automatically (kilometres and price per litre for the metric units, miles and price per gallon for mpg).
- Enter the trip distance. The total length of the journey, e.g. 300. For a round trip, double the one-way distance.
- Enter the fuel efficiency. For example 14 km/L, 7 L/100km, or 30 mpg. Use the figure for the kind of driving you’ll do — motorway runs are usually more efficient than stop-start city traffic.
- Enter the fuel price. The price per litre (or per gallon for mpg), in your own currency, e.g. 1.60. Leave it blank to see just the fuel needed.
- Read the results. The cards show the fuel needed for the trip, the total trip cost, and the cost per kilometre (or per mile) so you can compare journeys.
Every card recalculates the instant you change a number or switch the unit, so you can compare cars, routes or fuel prices without pressing a button.
The formula behind the numbers
Fuel cost comes down to two steps: how much fuel the trip uses, and what that fuel costs. The fuel used is the distance divided by the efficiency, so the headline formula iscost = distance ÷ efficiency × price. The calculator handles the unit maths for you — forlitres per 100 km it multiplies the distance by the litres-per-100 figure and divides by 100, and formiles per gallon it converts gallons to litres and miles to kilometres so the numbers line up. A 300 km trip at 14 km/L needs 300 ÷ 14 ≈ 21.4 litres; at 1.60 per litre that is about 21.4 × 1.60 ≈ 34.30.
Why estimate fuel cost in advance
- Budget a road trip: know the fuel bill before you leave, and split it fairly between passengers.
- Compare routes: a shorter motorway route at higher efficiency can beat a longer scenic one — the cost-per-km figure makes the trade-off clear.
- Compare vehicles: enter the same trip with two different efficiency figures to see how much a thirstier car really costs.
- React to prices: when pump prices move, re-run the trip to see the real impact on your wallet.
The estimate assumes a steady average efficiency for the whole trip. Real-world consumption swings with traffic, speed, load, air conditioning, terrain and weather, so treat the result as a solid planning figure rather than an exact total. For the most accurate number, use the average efficiency your car reports over similar journeys.
Is it private?
Yes. The Fuel Cost Calculator is plain JavaScript that runs entirely inside your browser tab. The distances, efficiency figures and prices you type are never uploaded, logged or stored anywhere — there are no accounts and no tracking of your inputs. Once the page has loaded you can even use it offline.
Frequently asked questions
How do I convert between km/L, L/100km and mpg?
You don’t need to — just pick the unit your car uses and the calculator converts internally. For reference, litres per 100 km is 100 divided by km per litre, and US mpg is about 235.2 divided by the L/100km figure. The tool uses 1 US gallon = 3.7854 litres and 1 mile = 1.609 km.
What currency does it use?
Whatever you like. The calculator is currency-neutral: it multiplies the fuel volume by the price you type, so the cost cards come out in the same currency as your fuel price.
Does it use US or UK gallons for mpg?
The mpg option uses US gallons (3.7854 litres). A UK gallon is larger (4.546 litres), so if your figure is UK mpg, multiply it by about 0.833 before entering it, or switch to a metric unit instead.
Estimates assume a steady average fuel efficiency and a flat fuel price; real consumption varies with driving conditions.