Ported subwoofer box volume?

Okay so I was wondering when you calculate the volume of a ported box does the volume of the port also count as volume of the box? Like a box 2.5 cubic feet with the port, or a 2.25 with the port in, but the port doesn't count as part of the volume of the box. They say when you make a box if its 2.5 cubic feet, then calculate the port and add the port displacement to the box. Could anybody shed some light on this? If there's a website with this answer let me know, thanks