Price a drive before you take it: distance, the vehicle’s MPG, and the local fuel price give the total fuel cost.
Fuel needed = distance ÷ MPG, and cost = gallons × price per gallon. Real trips usually run a little higher than the estimate — detours, traffic, and air conditioning all add a few percent, so treat the result as a floor rather than an exact figure.
Should I use city or highway MPG? Use the figure that matches most of the trip. For a mixed drive, the combined rating is the honest middle.
How much buffer should I add? About 10% covers detours and price differences between stations along the way.