I stayed in one when travelled solo. Don't know if they are all the same. Mine had a twin and a bed that folded down from the wall. Might be close for 2, but it was enough. Cheap way to travel. Didn't spend a whole lot of time in it. But then, I don't spend much time in any inside cabin.
We have often done 1A cabins on Carnival and they were fine. 2 singles that can be put together for queen size. I suggest going to their website for exact footage, but on the ships we have been on in the last 10 yrs, there never seemed much difference in size until you jumped up to a much higher category.
This was not true on their older ships, but a lot of things have changed, some even for the better!