Is 13 A Good Number ?

[t-roy]

is 13 a good number of in. per sq. foot of box for a slot port? and by 26 long? do you take the cubic ft you need and divide it or make it bigger and port to that displacement. example need 3.0 sq box so do i build it about 4.2 and port for that and after dis. of port, subs, dub. baffle and some 45's im right around 3.0 or do i figure the port for the 3.0 and just add that to the 3.0 but my thing is this will give you 2 diffrent numbers when you take it times the 13 and divide by the height of what the port will be just wanting to know the port will be 14.5" tall so @ 3.0 and then figure the port it will be 2 3/4 so do i just add the .60 to the 3.0 because it will be 2.75 x 14.5 x 26 .59 cube but all that confusion whatever, i just need to know do i fig the port for a box 3.0 what i need and the just add the dis of the port subs ect.. or do i fig the port for the box size it will be after all the displacements ? man i'm confusing myself i just can't type what i'm thinking , i'm tired. i think i have it in my head