Car manufacturers advertise a vehicle's gas mileage to potential buyers. However, the gas mileage you get driving the car may differ from the manufacturer's estimate. Determining your actual gas mileage allows you to more accurately calculate your gas costs. Knowing exactly how much it costs you to drive your vehicle per kilometer may spur you to reduce costs. Keeping your tires inflated, removing excess weight from the trunk, and receiving routine maintenance may improve your overall gas mileage and reduce your cost per kilometer.
Things You'll Need
 Calculator

Drive your vehicle until the fuel tank is empty. Completely fill the tank with gas. Write down the number of gallons you put into the tank and the total cost.

Reset your trip odometer to zero.

Use your car as you normally do. Avoid driving more highway or city miles than you typically do, because it can alter your gas consumption. Drive the vehicle until the fuel tank is empty again.

Check your trip odometer to find the total number of miles you drove. Use a calculator to convert miles into kilometers. Multiply the number of miles you drove by 1.61. For example, driving 350 miles is equal to 350 * 1.61 = 563.5 kilometers.

Divide the cost of gas by the number of kilometers you drove. For example, if the tank of gas cost $63, divide $63 by 563.5 kilometers, yielding 0.11. Multiply this number by 100 to find the cost of gas in cents per kilometer. Driving the example vehicle shown above costs you 11 cents per kilometer you travel.
Tips & Warnings
 To reduce the cost per kilometer of driving your vehicle, keep it in good condition and drive in a smooth, controlled manner. Speeding and frequently stopping and starting reduce your gas mileage, increasing the fuel cost per kilometer.
 Basing your gas cost calculation on one tank of gas may be slightly inaccurate. For a more accurate measurement, calculate your gas costs based on five or more tanks of gas. Increasing your sample size reduces the impact of an event that caused you to guzzle more gas than usual.
References
 Photo Credit Jupiterimages/Photos.com/Getty Images