i know the difference between square vent and a slot port. i think

and i know how the slot port will be shorter because the air keeps traveling 1/2 the width of the port...

but how do you figure the length up if the port only uses one side of the box instead of 3 like the average slot port?

i know it wont make that big of a change in tuning maybe 1-2 hertz but i was just wondering.