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ToolBoxGenie

Fuel Cost Calculator

Calculators · Added 14 August 2026

Enter a distance, your vehicle's efficiency and the current fuel price, and this calculator returns the fuel needed, what the trip costs, the cost per kilometre and the return figure. It handles km/l, mpg in both UK and US gallons, and l/100km — units that run in opposite directions and are easy to mix up.

Higher is better on this unit.

Splits the total.

How to use the fuel cost calculator

  1. 1Enter the distance and choose kilometres or miles.
  2. 2Enter your vehicle's fuel efficiency and pick the matching unit. The hint tells you whether higher or lower is better for the unit you chose.
  3. 3Enter the current fuel price per litre.
  4. 4Set how many people are sharing, if you want the cost split.
  5. 5Press Calculate to see the litres needed, the one-way and return cost, and the cost per kilometre.

Examples

A long drive

Input
500 km at 18 km/l, fuel at ₹105 per litre
Result
27.78 litres · ₹2,916.67 one way · ₹5.83 per km

The return trip doubles it to ₹5,833.33, which is the figure worth comparing against a train fare.

Splitting a road trip

Input
The same trip with four people sharing
Result
₹729.17 each one way

Per-person cost is what makes driving competitive on a long route. Alone it rarely is.

A car quoted in mpg

Input
300 miles at 45 mpg (UK), fuel at ₹105 per litre
Result
About 30.3 litres · around ₹3,180

The same car is about 37.5 mpg in US gallons. The two gallons differ by 17%, so the unit matters.

About the fuel cost calculator

The unit trap

Fuel efficiency is expressed in two incompatible ways, and the difference causes more errors than the arithmetic ever does. Distance per volume — kilometres per litre, miles per gallon — improves as the number rises. Volume per distance — litres per 100 kilometres, the standard across much of Europe — improves as the number falls.

The consequence is that you cannot compare the two by inspection, and averaging them is meaningless. It also means efficiency gains are not linear in the way people assume: improving from 10 to 15 km/l saves far more fuel over a given distance than improving from 30 to 35 km/l, even though both are a five-unit gain. The l/100km convention exists precisely because it makes that relationship obvious.

The gallon problem compounds it. UK and US gallons differ by about 17%, so an mpg figure is meaningless without knowing which gallon it refers to. This calculator asks explicitly rather than guessing, because a silent default here would produce a confidently wrong answer.

What actually determines the number

Speed is the largest controllable factor on a long drive. Aerodynamic drag rises with the square of speed, so the energy needed to overcome it rises steeply — the difference between 80 and 110 km/h on a motorway is substantial, and it is why fuel consumption on a highway trip is so sensitive to how hard you drive rather than how far.

In town the picture inverts. Drag barely matters at low speeds; what dominates is the energy repeatedly put into accelerating the vehicle's mass and then discarded as heat under braking. This is why city figures are worse than highway figures for conventional cars, and why hybrids reverse that ordering by recovering some of the braking energy.

Everything else is smaller but cumulative: tyre pressure a few PSI low costs a percent or two, a roof box costs more than most people expect at speed, air conditioning draws real power, and unnecessary weight in the boot is carried on every journey. None of these is dramatic alone; together they explain most of the gap between a brochure figure and a real one.

Frequently asked questions

Which efficiency unit should I use?
Whichever your vehicle is quoted in, and take care of the direction. km/l and mpg are distance per volume, so higher is better. l/100km is volume per distance, so lower is better. The calculator converts all of them to a common basis internally, and the hint under the field reminds you which way round the one you picked runs.
Why do UK and US mpg differ?
Because the gallons differ. A UK imperial gallon is about 4.546 litres and a US gallon is about 3.785 — a 17% gap. The same car quoted at 45 mpg in the UK is about 37.5 mpg in the US, with no change to the vehicle. Mixing them up produces an error large enough to matter over a long trip.
Why is my real consumption worse than the brochure figure?
Manufacturer figures come from standardised test cycles that are gentler than real driving. City traffic, high speeds, air conditioning, roof loads, under-inflated tyres and hilly terrain all reduce efficiency, sometimes by a wide margin. Calculating your own from a full tank and an odometer reading gives a far better number than any published figure.
How do I measure my own efficiency?
Fill the tank completely, note the odometer, drive normally until you are low, then fill completely again and note both the odometer and the litres taken. Distance travelled divided by litres added gives km/l for that stretch. Repeat over a few tanks — a single measurement is noisy.
Does this include the full cost of driving?
No, fuel only. Tolls, parking, tyre and brake wear, servicing intervals that arrive with distance, and depreciation are all real costs of a trip and none of them are here. For a genuine comparison against a train or a flight, fuel is the floor rather than the total.

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