Below is the approximate Pashtun population of Pakistan. The population of FATA has been grossly understated in Census 2017 (IDPs during operation in South Waziristan exceeded 1.5 million). According to my calculation the population of FATA has to be around 8-10 million. Furthermore, the percentage in my estimation of Pashtuns in non-Pashtun areas has also been very conservative, however, i am of the opinion that the below numbers give us some idea of the population of Pashtuns in Pakistan.
I have come across many studies that puts Pashtun population solely in Karachi at around 7 million. Furthermore, in case of Punjab, there is Pashtun indigenous population in Attock and Mianwali district, in addition to the migration of Pashtuns to major cities of Punjab due to economic reasons. Finally, war on terror has pushed many pashtuns to Sindh and Punjab which has to be considered.