What are the differences between studio apartment and efficiency unit?

Answer 1

A one-bedroom apartment has one room designated specifically as the bedroom (and others for kitchen and/or living space.) An efficiency apartment combines all of those into one room, with only the bathroom being separated by walls/doors.

Answer 2

1. Efficiencies are small living spaces, while studios can often be larger. 2. Efficiency apartments have a reduced-size kitchen (area), perhaps even just a hot plate instead of a stove/range.
3. The word studio may also refer to an artist's quarters used chiefly for making art, and so may not even contain sleeping arrangements.