Don't have the measurements but they are not big. In rooms with the split bathrooms there are shelves next to each sink. If you Google DCL stateroom bathrooms you'll find many photos.
I bring a mesh foldable bathroom caddy and store it under the sink. We also bring a mesh shower organizer that hangs on the shower hooks. These two things help a lot.
I've found them to be MORE than adequate. Would have sworn I had pictures of them packed with stuff, but I can't find them. I always bring little organizey things, but never need them.
Now. I am the only female in our room, and that might make all the difference.
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