A worked example: 250 km at 18 km/l, ₹100/liter
A 250 km trip in a car that does 18 km per liter, with fuel at ₹100 per liter, needs 13.89 liters and costs ₹1,388.89.
The formula: distance ÷ mileage × price
Liters needed = trip distance ÷ vehicle mileage. Fuel cost = liters needed × fuel price per liter. Two straightforward steps, but each input matters — a wrong mileage figure throws off the liters estimate, which then throws off the cost estimate too.
A thirstier vehicle over a longer distance: 600 km at 12 km/l, ₹105/liter
A 600 km trip in a less fuel-efficient vehicle (12 km/l) with slightly pricier fuel (₹105/liter) needs exactly 50 liters and costs ₹5,250 — nearly 4× the first example's cost, driven by both the longer distance and the lower mileage compounding together.
Why highway vs. city mileage figures matter
A vehicle's real-world mileage differs meaningfully between highway and city driving — using a city mileage figure for a highway-heavy trip understates how far a tank of fuel actually goes, and overestimates the fuel cost. Using the mileage figure that matches the actual trip's driving conditions gives a more accurate estimate.
What this calculator leaves out
This covers fuel only — tolls, food, and lodging for a multi-day trip aren't included here, though they use the same underlying cost logic in the fuller Road Trip Cost Calculator. Adding a 10-15% buffer to the fuel estimate is also worth considering, to account for detours, traffic idling, or AC usage on an unfamiliar route.