Studio is a pretty broad term. It can be a single workstation, a cube or a single room, and then studios would be a cluster of workstations, cubes or rooms. People can also use the word studio to refer to an entire building in which art takes place.
I looked it up on Dictionary.com, and it seems the smallest unit they define as a studio is a single room:
An artist's workroom.
A photographer's establishment.
An establishment where an art is taught or studied: a dance studio.
A room, building, or group of buildings where movies, television shows, or radio programs are produced.
A room or building where tapes and records are produced.
A company that produces films.
A studio apartment.
So I guess if you have more than one room with full design amenities, you have studios, and if you have a single space with all amenities available, you have a studio.