Intensity is a physical property of the sound. It is measured by observing its effect on a physical instrument and is described numerically. It is the same whether anyone is listening to the sound or not. Loudness is the subjective perception of the intensity. In other words the impression the sound makes on a listener. Loudness is not measured physically but is described in words such as “soft”, “loud”, “can barely hear it”, or “incredibly loud”. Different people listening to the same sound may describe its loudness differently. A hearing-impared person, for example, may judge a certain sound to have low loudness, while a normal-hearing person listening to the same sound may judge it to be loud. Loudness increases when the intensity increases but not linearly. Loudness depends in a complex way on several properties of the sound besides intensity, such as the sound’s frequency and variation with time.

Loudness depends apon amplitude of the wave. Higher the amplitude, higher the loudness.The amount of sound energy passing each per unit area is called intensity of sound