Glossary  >  Decibel (dB)

Decibel (dB)


The Decibel (dB) is a unit of measurement equal to 0.1 (or one-tenth) of a bel (B). It indicates the ratios of two physical quantities, typically acoustic power or electric signal on a logarithmic scale.

This means that two signals, whether electric or acoustic, whose levels vary by one decibel have a power ratio of 101/10 or a root-power ratio of 101/20.

Note: Decibels indicate power ratios, not amounts.

The bel (B) was coined in honor of Alexander Graham Bell, inventor of the telephone, but is rarely used. Instead, the decibel is more commonly used in different applications, such as to denote the gain or loss of amplifiers, attenuation of signals, and signal-noise ratios.

Note: The decibel is nonlinear because it’s a logarithmic unit. For clarity, here’s a table comparing power loss and gain ratios against decibels.

Loss/gain as a ratio Loss/gain in decibels Loss/gain as a ratio Loss/gain in decibels
1000 30 dB 0.1 -10 dB
100 20 dB 0.01 -20 dB
10 10 dB 0.001 -30 dB
1 (no loss or gain) 0 dB 0.0001 -40 dB

Example of Decibel (dB) in a sentence

"Sound waves traveling through the air attenuate by 6 dB for a doubling of distance when the sound comes from a single source."

Related Terms for Decibel (dB)

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