In terms of transportation "fuel efficiency" is more commonly refers to the energy efficiency of a particular vehicle model. It is the ratio of distance units per unit amount of input fuel (gasoline, diesel, petrol etc.). Given here is the petrol consumption per km formula to estimate the cost of petrol for travelling to a particular distance. Also, based on the consumption you can calculate the petrol cost per kilometer using the fuel cost per km formula.
Feel free to make use of this petrol consumption per km formula to calculate the petrol consumption of your vehicle. And this fuel cost per km formula helps you to plan your budget for the fuel cost and allowances.