Calculating Dual Round Ports?

[kfx450r]

When putting in 2 round ports. Lets say for example you have 2x Round Ports each like 3" diameter and a port calculator says 30"

Would each port be 30" long or would you divide the length between them so each is 15" long?

I have 4x 2" Round Ports and it says like 37" So would each have to be 37" long or 9" long (divided about 4 ways)

[Torres]

if in the calculator you put that you have 4 ports, each port will need to be 37" long.