There are many ways to calculate fuel consumption of your car. Manufacturers calculates it using following fuel consumption formulas:
Urban consumption: The urban cycle is performed at an ambient temperature of 20o C to 30o C in a laboratory. Test begins with a cold start. During the test, vehicle performs accelerations, idling and driving at constant speed. Vehicle reaches 50 kilometers per hour as maximum speed, average speed 19 kilometers per hour and the covered distance is 4 kilometers.
Extra-urban consumption: The cycle begins just after urban cycle and contains semi-constant speed driving with acceleration, decelerations and idling. Vehicle reaches up to 120 kilometers per hour as maximum speed, average speed is 63 kilometers per hour. During test, covered distance is 7 kilometers.
Combined consumption: 37% of urban cycle and 63% of extra-urban cycle values are summed up for the combined fuel consumption value.