Help with port tuning

I am wondering if anyone can help me. I need help finding out how long a port has to be to achieve the right tuning. I am new to the ported box thing. I have always went with sealed boxes. I have read a tutorial on finding out how big of diameter the port has to be but I cant find a tutorial on how long it has to be to tune it. If someone can help me out with the calculations I would greatly appreciate it.

Thanks
J.T.

 

Thanks for the program