Calculating SPL from voltage output of a microphone with MAX4466 amplifier
Microphone sensitivity is quoted at 


  -44 ±2 dB, f = 1KHz, 1Pa 0dB = 1V/Pa


This means that for 1 Pa RMS sound pressure on the microphone you get -44 dBV RMS at 1kHz. Still confused?

Well, -44 dBV translates to \$10^{-44/20}\$ volts = 6.31 mV RMS and 1 Pa translates to a decibel sound pressure level of 94 dB SPL.

So your microphone produces a 1kHz sinewave of amplitude 6.31 mV RMS when subjected to a SPL sinewave of 94 dB.

As for the gain of the Maxim circuit, without a circuit diagram I can't help you any further.