Very subjective.
1. Depends on the type of car.
2. Car weight, number of people in the car
3. Is the car serviced
4. Time of day
5. City or highway driving
6.

Hear those car companies, usually, use a very skinny test driver, with minimal car weight and test drive during very cold hours of the day to get their optimum fuel consumption figures. So, Fuel consumption figures in the car brochures only look good but might not be so accurate in real life.

To get an accurate fuel consumption figure, you should download an app like Fuel Buddy.