Round-trip fuel cost: count both directions once
Build a complete trip distance before multiplying consumption by the fuel price.
Method
First decide whether the distance entered is one way or already the round trip. For a return along the same route, double a one-way distance exactly once. Then litres used = total KM × L/100 KM ÷ 100, and fuel cost = litres × price per litre. Add detours to the distance before calculating. A fuel-cost estimate is separate from parking, tolls and fixed ownership expenses.
Worked example
The destination is 60 KM away and the return is another 60 KM, giving 120 KM. At an assumed 6.5 L/100 KM, fuel use is 120 × 6.5 ÷ 100 = 7.8 L. With an illustrative price of 2.20 per litre, cost is 7.8 × 2.20 = 17.16 in the price’s currency. If your route planner already displays 120 KM for the entire journey, do not double it again.
What to check
Use Fuel economy to derive consumption from a representative distance and fuel quantity, or enter an explicit assumption. Different traffic, load and conditions can change actual consumption. Convert MPG to L/100 KM before using this formula, selecting US or imperial MPG explicitly. A quoted price per gallon must also be converted to a price per litre. The example price is hypothetical, not a live fuel quote or a guaranteed trip bill.