The loudness of sound is measured in units called decibels (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. Normal speech is around 50 to 60 dB. The following chart demonstrates the sound scale in decibels.

When an individual is over-exposed to excessive loudness, sensitive structures of the inner ear, such as hair cells, can be damaged, causing noise-induced hearing loss (NIHL), a particular type of hearing loss.