Question

What is the SI unit of loudness?

Answer 1

The loudness of sound is measured in a unit called deciBel (dB). A deciBel unit expresses the relative intensity of sounds on a scale from zero for the average least perceptible sound to about 100 dB, which is near the level most people find uncomfortably loud.

The loudness level of a sound is a subjective, rather than an objective, measure. phon is the unit of loudness level. The unit phon is used to indicate an individual's perception of loudness. By definition, 1 phon is equivalent to 1 deciBel at 1000 Hz (1 kHz).