My dad has a very large penis, 9 inches erect. What is the chance that mine will be like his?
The size of your penis is determined by the genes you received from both your father and your mother -- just like other physical features of your body, such as the shape of your ears and the size of your nose. Not much is known about the precise nature of the inheritance of penile size, so odds can't be set.
As stated before, the size of man's penis has very little impact on his ability to have sex or how enjoyable is that sex. An overly large penis can be uncomfortable, at least initially, for a woman. So whether your penis is large should not be a concern.