Is First Floor ground floor?
Also to know is, which floor is the first floor?
In British English the floor of a building at street level is called the ground floor. The floor above it is the first floor and the floor below is called the basement. In American English, however, the floor at street level is usually called the first floor.
Considering this, which countries use ground floor?
In other countries, including Chile, Colombia and Peru, the ground floor is called primer piso (first floor). If planta baja is ever used it means the ground-level floor (although primer piso is used mainly for indoor areas, while planta baja is also used for areas outside the building).
Yes, one always says "on" the first floor. The only time you might say "at" is if you are arriving at a particular floor, perhaps via the elevator. But once you exit the elevator you are "on" the floor.