How to Calculate the Fuel Cost of a Road Trip (and Split It Fairly)

Before a road trip, it's useful to know roughly what you'll spend on fuel, both to budget and to split costs fairly with the people travelling with you. The maths is simple once you know three numbers.

The formula

Fuel cost = (distance ÷ mileage) × fuel price.

Say the trip is 350 km, your car gives 15 km per litre, and petrol costs ₹105 a litre. You'll need 350 ÷ 15 ≈ 23.3 litres, which costs about 23.3 × 105 ≈ ₹2,450. For a return journey, double it: about ₹4,900.

Cost per kilometre

Divide the fuel price by your mileage to get your cost per km: ₹105 ÷ 15 = ₹7 per km. This is handy for quick estimates, a 120 km round trip costs about ₹840 in fuel, and for comparing driving with a train or bus ticket.

Why your real mileage is different

The mileage figure in a car's brochure is measured in controlled test conditions. Real-world mileage is usually lower, and changes with:

• Speed: fuel use rises noticeably at high speeds because of air resistance.
• Traffic: stop-start city driving uses more fuel than steady highway cruising.
• Load and AC: passengers, luggage and air-conditioning all add to consumption.
• Tyre pressure: under-inflated tyres increase rolling resistance.
• Hills: climbing ghats uses far more fuel than flat roads.

To find your true mileage, fill the tank fully, reset the trip meter, drive normally, then fill up again. Divide the kilometres driven by the litres you added.

Don't forget the other costs

Fuel is only part of the trip cost. Add tolls (FASTag charges vary by route and vehicle type), parking, and food stops to get a realistic total.

Splitting it fairly

The simplest approach is to add up fuel, tolls and parking and divide equally. If someone joins for only part of the trip, you can split by the distance each person travelled instead. Settle up at the end rather than after every fuel stop, it saves a lot of small transfers.

Try it: the Fuel Cost Calculator works out your trip cost, the Bill Split Calculator divides it between everyone, and the Unit Price Comparator helps compare prices per litre or per kg.

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