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The minimum requirement of penis length for conceiving or healthy sex life is more than 2 inches when in erect position.The excess length is OK but it does not matter much because:
--there is less or no sensation of pleasure in vagina after a depth of 2 inches.
--for fertilization during pregnancy
the sperms have to travel to go to the ovum or egg & not the penis.
I hope the answer is helpful to you.