Problem about gain of Power Amplifier!

If I'd like to design a Power Amplifier,how can I estimate the enough gain?
Is it refer to the application or protocal?

depends on application
As per std in case of commercial product.

The Power Amplifier gain is part of the RF System analysis of the entire transmitter chain.
The gain and loss of each transmitter stage should be distributed from the modulator up to the antenna.
The gain of the power amplifier is limited by different factors, as stability, number of internal stages, input available power, etc.