Fuel tank driving range:
litres in the tank times kilometres per litre

Range from tank size and economy

If you know how much fuel you have and how far your vehicle travels on each litre, the maximum distance is the product of the two. A tank holding 35 litres in a car that returns 16 km/L can cover 560 km before running dry.

The formula works for any amount of fuel, not only a full tank. With 20 litres on board the same car has a range of 320 km.

Which economy number to use

The result is only as good as the km/L you feed in. A figure printed in a brochure comes from standard test conditions. Your own number, measured by filling the tank, driving normally and refilling, is better. Divide the kilometres driven by the litres added to get it.

Because fuel use varies, a range estimate is best given as a band. For this car, somewhere between 420 and 630 km is a realistic spread rather than a single number.

Usable fuel is not the same as tank size

The tank capacity in the specification is the total volume, but the last few litres are not meant for planning. The low-fuel warning typically comes on with several litres left, and running very low can stress the fuel pump. Many drivers refuel at one-quarter tank.

A simple rule is to hold back 10% of the tank as a reserve. For the 35 L tank that is 3.5 litres, so the planning range is 31.5 × 16 = 504 km. In remote areas, long hill sections, or places where fuel stations are far apart, a larger buffer makes sense.

What moves the km/L up or down

• Speed: consumption rises noticeably at high highway speeds because of air resistance.
• Load and roof racks: extra weight and drag reduce economy.
• Tyre pressure: under-inflated tyres increase rolling resistance.
• Terrain and traffic: hills and stop-start driving use more fuel per kilometre.
• Air conditioning and engine health: both can shave a few per cent off economy.

These effects add up. A car that does 16 km/L on a calm highway might manage 12 km/L in a stop-start city commute, which would cut a 560 km paper range to 420 km.

Working backwards to the fuel you need

The same relationship can be rearranged. Fuel needed equals distance divided by km/L. For a 560 km trip at 16 km/L you need 35 litres. For a 300 km drive you need 300 ÷ 16 = 18.75 litres, so about 19 litres plus a small reserve.

Multiplying the litres by the local fuel price gives the cost of the trip. A mileage calculator helps with the km/L itself, and a trip-cost calculator puts a rupee value on it using the price per litre you enter. Fuel prices change often, so use the figure at your pump.

Comparing two vehicles on range

Tank size alone does not decide range. A smaller tank in a more efficient vehicle can travel further than a larger tank in a thirsty one. A 40-litre tank at 11 km/L gives 440 km, while a 35-litre tank at 16 km/L gives 560 km.

Vehicle C carries the most fuel and has the longest range, but it burns more fuel per kilometre than B. Over a 600 km trip, C uses 50 litres while B uses 37.5. If fuel cost matters more than distance between stops, B is the cheaper car to run on long journeys.

Putting range and cost together

Once the range is known, the cost per kilometre follows from the fuel price. If a litre costs ₹100, a car doing 16 km/L spends ₹6.25 per kilometre, and a full 35-litre tank costs ₹3,500. A 560 km journey therefore costs about ₹3,500 in fuel.

The ₹100 is a placeholder; prices differ by city and fuel type and move often, so substitute the figure on your last receipt. The arithmetic is the same every time: litres needed × price per litre.

Build your own economy figure

The most reliable input is your own history. Note the odometer and litres at each full fill-up for a few weeks. Add up the distance and the litres, then divide. A running total smooths out the effect of one unusual trip and gives you a number for city use and another for highway, which you can use for different journeys.

If you notice the figure slowly falling over months, check tyre pressure, air filter and service intervals before assuming the engine is wearing out.

A note on EVs and hybrids

The same logic applies to electric vehicles, with kWh in the battery instead of litres and km/kWh instead of km/L. A 40 kWh usable battery at 6 km/kWh gives 240 km. Range drops in cold weather and at high speed, and many drivers plan to stop charging at around 20% remaining.

For plug-in hybrids, treat the electric and petrol parts separately and add the two ranges. The quoted combined figure assumes you start with a full charge and a full tank.