In this project we discussed the cooling load calculations for a commercial building by using revit software Window air conditioners, split air conditioners are used in small buildings and offices etc but in big buildings and commercial complex we use central air conditioning systems this systems are installed far away from the buildings. The cooled air is supplied to the building with the help of ducts. When ducts are not properly designed, then it will lead to problem such as frictional loss, higher installation cost, increased noise and power consumption. For minimizing this problem, a proper design of duct is needed. Equal friction method is used to design the duct; it gives the comparison of pressure drop in rectangular duct and circular duct. Central air conditioning is more reliable for easy operation with a lower maintenance cost. Cooling load items such as, people heat gain, lighting heat gain, infiltration and ventilation heat gain can easily by using REVIT SOFTWARE. The programme can also be used to calculate cooling load due to walls and roofs. And results were compared with the standard data given by ASHRAE and CARRIER. The RULE OF THUMB method is used to calculate the heat developed in the rooms. These methods are used for lower power consumption capital cost and improve aesthetics of building