decibel

WordReference Random House Learner's Dictionary of American English © 2025

dec•i•bel /ˈdɛsəˌbɛl, -bəl/   n. [countable]

1. Physics a unit that is used to express differences in power, esp. in measuring the loudness of sound. Abbr.: dB

WordReference Random House Unabridged Dictionary of American English © 2025

dec•i•bel  (des′ə bel′, -bəl), n. [Physics.]

1. Physics a unit used to express the intensity of a sound wave, equal to 20 times the common logarithm of the ratio of the pressure produced by the sound wave to a reference pressure, usually 0.0002 microbar.
2. Physics a unit of power ratio, the number of units being equal to a constant times the logarithm to the base 10 of the intensities of two sources.
3. Physics a unit used to compare two voltages or currents, equal to 20 times the common logarithm of the ratio of the voltages or currents measured across equal resistances. Abbr.: dB, db

• deci- + bel 1925–30

Collins Concise English Dictionary © HarperCollins Publishers::

decibel / ˈdɛsɪˌbɛl/ noun

1. a unit for comparing two currents, voltages, or power levels, equal to one tenth of a bel
2. a similar unit for measuring the intensity of a sound. It is equal to ten times the logarithm to the base ten of the ratio of the intensity of the sound to be measured to the intensity of some reference sound, usually the lowest audible note of the same frequency

Abbreviation: dB