http://www.cochlea.org/en/hear/human-auditory-range

Please keep in mind that decibel (which is equal to 1/10 Bel) is just a unit of ratio. A ratio alone tells you nothing about the magnitude of the value if you don't specify your reference level.

@Canina what is actually reference level?

Any decibel (or other fraction) value will be in relationship to something; that "something" is the reference value or level. For example, dBA SPL (which you'd probably see in relation to sound pressure levels) is not at all the same thing as dBm (decibel relative to 1 mW) or dBi (decibel relative to an isotropic radiator). Similarly, two camera lenses may both be, say, "3x zoom" but have hugely different focal length ranges, and thus capture very different images in usage.

Also, I have no idea how that extension might work (I don't use Chrome myself), but there's a myriad reasons why it wouldn't give actual measurements relative to some reference level, not least of which being that there's already a handful of adjustments that can be made before the sound even reaches the software.

@Canina suppose, if i code a software and, i take the mobile(which have that software) in a "silent" room(where i can't hear anything) and, if i put the dB level 0 or less than 0 somehow than is that correct measurement?