Wanderlust World Wanderlust World Write down the mileage indicated on your vehicle's odometer after filling the gas tank. The odometer tracts miles driven by the car and is located beneath the speedometer on the instrument panel. For example, the mileage might be 45,682 miles.
Record the number of gallons of gas required to refill the tank when it becomes empty. Also, write down the new odometer reading. Suppose the tank took 12 gallons and the odometer reading is now 46,018 miles.
Subtract the lower odometer reading from the higher one to obtain the distance traveled in miles. Continuing the example, you have 46,018 miles minus 45,682 miles, or 336 miles.
Divide the distance traveled by the fuel required to fill the tank to get the gas mileage of the vehicle in miles per gallon. Performing this step leads to 336 miles divided by 12 gallons, which equals a gas mileage of 28 miles per gallon.
Divide the total distance of your upcoming trip by the gas mileage of the vehicle to arrive at the number of gallons of fuel required. Suppose the total trip distance is 550 miles. Now you have 550 miles divided by 28 miles per gallon, or 19.6 gallons.
Multiply the number of gallons of fuel needed by the current price of a gallon of gasoline to obtain the total cost for the trip. For example, say the price of gas is $3.50 per gallon. Completing the example, you have 19.6 gallons times $3.50 per gallon, or $68.60.