How to Estimate Fuel Cost for a Trip

The formula

Fuel needed = distance × consumption ÷ 100. Trip cost = fuel needed × price per liter.

Example: 300 km in a car that uses 7 L/100km, with fuel at 1.70 a liter. Fuel = 300 × 7 ÷ 100 = 21 liters. Cost = 21 × 1.70 = 35.70.

The ÷ 100 is there because consumption is quoted per 100 km — it's the step people forget, and it's the one that makes the answer 100 times too big.

What L/100km actually means

It's the liters a car burns to travel 100 km. Lower is better. Typical figures: a small petrol car around 5–6, a family saloon 6–8, an SUV or diesel estate 8–11, a loaded van 10–14.

If your paperwork quotes kilometers per liter instead, convert it: L/100km = 100 ÷ km per liter. A car doing 15 km per liter uses 100 ÷ 15 = 6.7 L/100km.

Find your car's real consumption

The brochure figure is measured in a laboratory and is usually optimistic by 10–20%. Your own number takes five minutes to get.

Fill the tank, reset the trip counter, drive normally until you're back near empty, then refill and note the liters. Those liters are what you used for the distance on the counter, so consumption = liters × 100 ÷ distance. Do it three times and average, because one tank is heavily influenced by how much of it was motorway.

Cost per person and per kilometer

Divide the trip cost by the number of paying passengers to get a fair share — driver included, since the driver's fuel is not a discount to everyone else. Add wear and tolls if you're splitting a long trip regularly.

Divide by distance instead to get cost per kilometer, which is the number to use when you're working out mileage claims or pricing a delivery run. In the example, 35.70 ÷ 300 = 0.119 per km.

Price the drive before you leave

Enter distance, consumption and pump price into the Fuel Cost Calculator and it returns the liters you'll burn and the total cost.

To compare two routes, run the same two numbers with different distances — a 40 km detour at 7 L/100km and 1.70 a liter costs about 4.76, which is a useful thing to know before you call it the cheaper option.