Worked example: 350 km trip

Inputs: distance 350 km, consumption 7.5 litres per 100 km, petrol price $1.85 per litre. Fuel used = 350 ÷ 100 × 7.5 = 26.25 litres. Trip cost = 26.25 × $1.85 = $48.56 (rounded to cents).

Second check: 100 km at 8.0 litres per 100 km at $2.00 per litre uses 8.00 litres and costs $16.00. If you are splitting fuel with passengers, divide the trip cost by the number of people sharing it — for the 350 km example, four people sharing would pay $12.14 each. Round-trip costs are simply double the one-way figure if consumption and price are the same on the way back; in practice, allow a small buffer for detours and traffic.