Audio and DSP engineers rarely talk about absolute sound volumes.

Instead the preferred way of dealing with sound volume is relative to some reference.

The difference in volume between the signal being discussed and some reference is usually measured in decibels. Given a reference volume r and a signal volume x, the difference in volume is given by :

Often need to invert this :

For example, it is common to talk about a 'signal to noise' ratio. In this case the reference r, is the volume of the background noise and x would be the max volume of the signal. Typically look for SNR of 80dB or better.