Sir , I want to know. How to calculate a demand load of a particular area such as if having 3600sq.ft. area then how can we find out its load of lighting, power.

Give full details like type of usage whether office,store,shop,house,temple,workshop etc and dimensions (L,W,H) of building including air conditioning. If you provide a furniture layout and equipments(computers,copiers,sockets outlets etc) used with locations marked you can get better quotation/design.