How much square footage an office requires depends solely on the kind of business being carried out as well as the business size.
Some offices employ workers in shifts or part-time therefore their space requirements are lesser than most offices that have a large number of employees working throughout the day. Such offices not only need ample work space but also a reasonable break room or rest area for in between breaks.
A professional planner is usually able to determine the amount of space needed on the basis of number of employees and executives, size of business, working hours and site of the office. He also takes into consideration all washrooms, cafeterias, conference and recreation rooms before he makes a final estimate.
Similarly corridors, isles and hallways also form an integral part of the office and large offices today have vending machines, smoking zones and other facilities that add to the work atmosphere.