I have to disagree that you don't spend any time in your cabin. That might be the case for some people, but not for everyone.
We took our cruise with the intentions of spending a LOT of time by ourselves, relaxing on the verandah and generally being "antisocial". I know there were others on our sailing that felt the same way.
I would say I spent a full half of my waking hours in my cabin or on my verandah.
Back to the OP...the cabin width is the same as the verandah width. If your cabin is 9 feet wide, your verandah will be nine feet wide. They do seen to vary from about 8 feet wide to about 36 feet wide (the Walt/Roy suites). But generally speaking, cabins in category 4-12 will be between 8 and 10 feet wide. (The accessible rooms are different.) The biggest difference is in the length. The cat 11 and 12 rooms are only about 20 feet deep. The Cat four room is a foot or two wider, and is about 30 feet long. If the room includes a verandah, the square footage
DCL states for that rom includes the verandah, btw.
If you are really concerned about space, you should probably not wait until you get to the port, but upgrade now.
Anne