Fuel cost of a trip:
litres needed, rupees spent and cost per head

Three inputs decide the fuel bill

The distance comes from a map. The price per litre is on the pump. The mileage, kilometres per litre, is the one most people guess, and it is the input that changes the answer the most.

Distance divided by mileage gives the litres you will burn. Multiplying by the price turns litres into rupees. Everything else, such as tolls, parking and wear, is a separate cost you add if you want the full price of the journey.

A fourth input is worth adding for longer trips: the fuel price along the route. Pump prices vary between cities and states and are often cheaper away from highway service plazas. If your route crosses a state line, take the average of the prices at the start and end rather than assuming one figure for the whole journey.

The formula

The formula does not know whether your vehicle runs on petrol, diesel or CNG, so the price must match the fuel and its unit. For CNG, use kilometres per kilogram and the price per kilogram. For an electric car the same structure applies with kWh per km and the price per kWh, and the next step is to convert cost per km to a trip total.

If you are comparing several routes, calculate each one separately. A longer route on a good road at a steady speed can burn less fuel than a shorter one through towns, and the difference may not match the distance gap.

Worked example: 360 km on a highway

A return journey doubles the distance, so 720 km costs 48 × 105 = ₹5,040. If the same drive is done in stop-start traffic at 12 km/L, the fuel is 360 ÷ 12 = 30 L and the cost rises to ₹3,150, an extra ₹630 from nothing but conditions.

The result gives a handy rule of thumb for this car and price: every 100 km needs about 6.7 litres and costs about ₹700. Multiplying that by the distance in hundreds of kilometres is quicker than redoing the division each time.

What fuel alone leaves out

Fuel is the most visible expense of a drive, yet it is not the only one. Tolls on highways, parking at the destination and any overnight stay are separate lines. Over a longer ownership horizon, tyres, servicing and depreciation also scale with the kilometres, so many people quote a full running cost per kilometre that is considerably higher than the fuel-only ₹7.

For deciding whether to split a ride, fuel plus tolls is a fair basis, because those are the costs the trip actually causes. For comparing against a train or bus ticket, include the extras that are unavoidable, such as parking, to keep the comparison honest.

Finding your real mileage

The brochure figure is measured under test conditions. A more honest number comes from the tank-to-tank method, which needs no special equipment.

1. 1Fill the tank to the first click of the nozzle and reset the trip meter.
2. 2Drive normally for a few hundred kilometres.
3. 3Refill to the same level and note the litres added.
4. 4Divide kilometres driven by litres: 420 km on 28 L is 15 km/L.

Repeat the test for city and highway driving separately, because the two can differ by 20% or more. Use the figure that matches the trip.

Odometer and pump quantities can both carry small errors. A fill-up measured on a different pump or at a different tank level can shift one test by several percent, so average two or three fills before relying on the result. Many cars also display a running average on the trip computer, which you can compare against your tank-to-tank figure.

What pushes mileage up or down

A sample budget for a weekend drive

Replace the assumed figures with your own and the table becomes a working budget. Dividing ₹6,444 by four travellers gives about ₹1,611 each, which is a number everyone can agree on before the trip, not after.

Splitting the cost and budgeting the rest

• Share the fuel by distance travelled per person if people join or leave along the route.
• Add tolls and parking separately, since they do not depend on mileage.
• Include a margin of 10% for detours and traffic.
• Use the pump price at the start of the trip; prices can vary between cities and states.

A calculator lets you swap in a different car, a different mileage or a fuel price quickly. That is useful when choosing between taking your own vehicle and a hired one with a different efficiency.

A final check is to compare the estimate with the tank. 24 litres for 360 km on a 40-litre tank leaves 16 litres in hand, or about 240 km of range, which means one refuel stop is not needed for the outward leg but is wise before heading back.

If you track expenses, record each trip with distance, litres and rupees. After a handful of entries you will have your own cost per kilometre for city, highway and mixed use, which makes the next estimate a single multiplication.