As of 2012, Greater Tehran had a population of close to 14 million residents.

[3] The 2016 census had the population at 13.3 million in Tehran Province (only 200 thousands of them outside Tehran and the suburban counties) and 2.2 million in Karaj and Fardis combined.

So it can be estimated that the population of the urban agglomeration was about 15 million people in 2016, and it is sinking 25 cm per year because of the accelerated influx and the overuse of natural resources.

[4] Since the 1960s, much of Greater Tehran's growth has been caused by an influx of urban poor into informal settlements on the fringe.

There is no exact definition of Tehran agglomeration borders and composition.