There can be, but it depends upon how you are doing the reading of the data, and what device you are reading from. It is not uncommon that the readings would be normalized to [-1, +1) or [-1, +1], or to 0 meaning no signal and ((2^bits)-1) meaning maximum signal that the ADC is configured to measure.
Usually when you want to know this kind of information, you also need to know the microphone pressure to signal curve. Most often the best way to get that is to calibrate with a reference source.
