Please indicate methods of measuring fuel efficiency in petrol driven cars?

Question

Please indicate methods of measuring fuel efficiency in petrol driven cars?

Answer 1

by smoke emission test. it tells that combustion is good if the result is within standard and it is fuel efficient.

Answer 2

Fill up your tank and reset your tripometre.  When you fill back up the next time, record your mileage as well as the amount of fuel required to refill the tank.  Do this over several tanks to get a good average and that will be your fuel mileage.