it depends on the distance and the power with which the module transmits and the antenna used for transmitting... without these details it is impossible to find....
At system level Signal strength is measured/specified more as a relative term than as an absolute one...i mean we generally express it as a ratio with respect to the Tx signal i.e.,
P(dB)=10log(Pi/Ptr)------(1)
or yet another way is...
P(dBm)=10log(Pi/1mW)----(2)
I mean they generally specify in terms of either equations and Pi is then calculated easily.....!!
i am going to add on to waht was posted already that a lot goes into signal strength which are how many watts are you pushing and the hight of your antenna. Those two factors are your biggest concerns.