Question Summary:
i want to know what is the minimum length of male private part one should have to be able to have intercousre with his wife according to shariah?

Question Detail:

i want to know what is the minimum length of male private part one should have to be able to have intercousre with his wife according to shariah and what can be done to increase the length of the penis

Answer :

In the name of Allah, Most Gracious, Most Merciful
Assalaamu `alaykum waRahmatullahi Wabarakatoh
There is no minimum requirement for this in Shariah. 
And Allah knows best
Wassalam
Muhammed Zakariyya Desai,
Checked and Approved by:
Mufti Ebrahim Desai
Darul Iftaa, Madrassah In'aamiyyah