Decibel (dB)

A decibel is a unit used to measure the intensity (loudness) of sound. The decibel scale is logarithmic, not linear. An increase of 10 dB represents a tenfold increase in sound intensity and roughly a doubling of perceived loudness. Soft sounds like rustling leaves register around 20 to 30 dB. Normal conversation sits around 60 dB. A lawnmower operates at approximately 90 dB. Sounds above 85 dB can cause noise-induced hearing loss with prolonged or repeated exposure.

In audiology, hearing thresholds are measured in dB HL (hearing level), a standardized scale calibrated to what normal-hearing adults detect. Results on an audiogram show how loud a sound must be at each frequency before a person can hear it. Degrees of hearing loss are classified by threshold ranges: normal (0 to 25 dB HL), mild (26 to 40 dB HL), moderate (41 to 55 dB HL), moderately severe (56 to 70 dB HL), severe (71 to 90 dB HL), and profound (91 dB HL or greater).