-Zaki K.
ANSWER:
There are many factors that will lead to determining the size that a restroom must be in a restaurant and the size will vary accordingly.
The clear floor space for a water closet, lavatory, accessories, toilet compartments, paths of travel, door maneuvering clearance, and turning space that are all requirements that will lead to the minimum size requirements.
I would suggest consulting with an architect.
I hope this helps!
-Brad
