Hello Mr Chan!
Coverage (or Signal Propogation) is not determined by the access point but by the environment in which it is installed. E.g. in a wide open space with an AP installed at height, this will allow signals to travel much further than in an internal, cluttered space with thick stone walls and an AP installed in a cupboard at knee-height.
You will need to use a Wi-Fi design tool such as Ekahau, AirMagnet, Yagna, Intangi Iris, etc. in order to calculate wall and clutter attenuation and estimate/predict signal propogation.
For further assistance I would recommend you speak to a Ruckus partner: https://extapps.commscope.com/howtobuy/RuckusChannelPartner
I hope that helps,