Calculate required air conditioner BTU (cooling capacity).
How big of an air conditioner do you need to cool a room?

Use this page to roughly calculate BTU (cooling capacity) of an air conditioner you need to cool your room depending on room size and characteristics.

Formula is pretty simple and it gives you an estimate of the cooling capacity your air conditioner needs to be in order to cool the desired room.
Formula multiplies volume of the room in cubic feet by 2.5; add 1,000 BTU for every window in the room, and 400 BTU for every person (occupant) in the room.  

Please specify the following information for the room:
Room width: ft
Room length: ft
Room height: ft
Room volume: ft3
Number of windows: window(s)
Number of occupants: occupant(s)
BTU (cooling capacity): BTU