Once you get an Athena username and can therefore get
certificates, you can access the
floor plans for every building at MIT.
But to answer your question, a quad is four people in one room. None of the personal rooms in MIT dorms are more than one room -- even dorms that have suites have personal bedrooms with shared suite space like a lounge, kitchen, and bathroom. But the Baker quads are fairly big rooms, at least -- they don't feel super-crowded, at least not in the limited time that I've spent hanging out in some.