The mileage of an AdBlue® tank depends on several parameters such as the capacity of the tank and the type of driving. Standard mileage is given by the manufacturer but your way of driving will affect this.
AdBlue® is a liquid consisting of 32.5% high-quality urea and 67.5% demineralised water.
The quantity of AdBlue® necessary depends on European environmental legislation which will most certainly evolve. Manufacturers have to adapt the consumption of AdBlue® in order to respond to changes in environmental standards.