How this is worked out
The arithmetic is one division and one multiplication:
litres = distance ÷ km per litre · cost = litres × price per litre
300 km at 18 km/l needs 16.67 litres. At ₹105 a litre that trip costs ₹1,750, or ₹5.83 a kilometre.
The part worth reading twice is the unit. India quotes mileage as kilometres per litre, where a bigger number is better. Europe and Australia quote litres per 100 km, where a smaller number is better. These are reciprocals of each other, not variants of the same measure, so the numbers run in opposite directions — and someone comparing an Indian brochure with a European one without converting will reach exactly the wrong conclusion.
18 km/l is 5.56 L/100km. It is also 42.3 MPG (US) and 50.8 MPG (imperial), and those two differ from each other because a US gallon is 3.785 litres and an imperial gallon is 4.546 — a 20% difference in the gallon, and therefore in the MPG figure, for the identical car. The conversion table under the result shows all four at once so a spec sheet in any of them can be read.
Everything runs in your browser. No location lookup, no live price feed, nothing sent anywhere — which is also why the price is a placeholder rather than today's rate.
A worked example
- Trip distance
- 300 km
- Mileage
- 18 km/l
- Fuel used
- 16.67 litres
- Price
- ₹105 a litre — a placeholder
- Trip cost
- ₹1,750
- Cost per kilometre
- ₹5.83
- Annual cost at 12,000 km
- ₹70,000 — ₹5,833 a month
- A car at 14 km/l instead
- ₹90,000 a year — ₹20,000 more
- 18 km/l in other units
- 5.56 L/100km · 42.3 MPG (US) · 50.8 MPG (imperial)
km/l and L/100km run in opposite directions
A car that does 18 km/l uses 5.56 litres per 100 km. Improve it to 20 km/l and the consumption falls to 5.0 L/100km. The first number went up and the second went down, and both describe the same improvement — because one is distance per unit of fuel and the other is fuel per unit of distance.
This matters whenever an Indian buyer reads a European or Australian review, or an Indian spec sheet is compared with an imported one. "7.1 L/100km" is not worse than "18 km/l"; it is worse than 14.1 km/l, which is what it converts to. Reading the two as though larger were always better gets the comparison exactly backwards.
There is a second, subtler consequence. Because km/l is a ratio of distance to fuel, equal steps in km/l are not equal savings. Going from 10 to 12 km/l saves far more fuel over the same distance than going from 20 to 22 — 1.67 litres per 100 km against 0.45. If you are choosing between two upgrades, the L/100km figure is the one that tells you which saves more fuel.
Why the price here is a placeholder and nothing else would be honest
Petrol and diesel are outside GST. They carry central excise duty plus a state VAT or sales tax that every state sets for itself, which is why the pump price differs by several rupees a litre between neighbouring states and by more than ten across the country.
On top of that, oil marketing companies revise retail prices daily. Any figure printed on a page like this is stale within a day and wrong for most readers on the day it is written, so this page defaults to a round ₹105 and says plainly that it is a placeholder.
The practical version of this: keep the last pump receipt. Type that price. If you fill in one state and drive through three, use the price you actually paid rather than an average, because the calculation is about your money rather than about the national picture.
Brochure mileage against the mileage you get
The figure on the brochure is measured by ARAI on a standard test cycle. It is reproducible and comparable between cars, which is its purpose. It is not a prediction of your commute, and the gap is routinely several km/l.
What closes or widens the gap: city traffic with frequent stops, air conditioning, roof carriers, underinflated tyres, short trips where the engine never warms, and a heavy right foot. None of these is exotic and together they account for most of the difference people notice between the brochure and the tank.
Your own figure is easy to establish and beats any published one. Fill the tank, note the odometer, drive normally, fill again, and divide the distance by the litres added. Do it twice and use the lower number — that is your real mileage, and it is the number to put in this calculator.
What the difference between two cars actually costs
At 12,000 km a year and ₹105 a litre, a car at 18 km/l costs ₹70,000 in fuel and one at 14 km/l costs ₹90,000. The gap is ₹20,000 a year, which over a five-year ownership period is ₹1,00,000 before any fuel-price rise.
That is enough to change a purchase decision, and it is also enough to be swamped by the other running costs, which is why fuel alone should not decide it. Insurance, service intervals, tyre cost, and the resale difference between a petrol and a diesel variant are all in the same order of magnitude.
The comparison this page does is deliberately narrow: fuel, at your distance, at your price. Use it as one input. A CNG or electric alternative changes the arithmetic entirely — different fuel, different unit, different tax treatment — and is not something a km/l comparison can answer.
Assumptions and sources
- Unit conversions
- 1 US gallon = 3.785411784 litres, 1 imperial gallon = 4.54609 litres, 1 mile = 1.609344 km — all exact definitions. Verified in tools/test/work.mjs with round-trip checks.
- km/l to L/100km
- L/100km = 100 ÷ km per litre. 18 km/l = 5.56 L/100km, 42.3 MPG (US), 50.8 MPG (imperial). Computed by this page from assets/js/tools/work.js.
- Fuel prices
- NOT a source of fact. The ₹105 default is a placeholder so the page computes something on load. Petrol and diesel are outside GST, taxed by each state, and revised daily by the oil marketing companies. checked 2026-09
- Brochure mileage
- ARAI test-cycle figures are measured on a standard cycle for comparability between vehicles, not as a prediction of real-world consumption. Use your own tank-to-tank figure where you have one.