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     on matters related to measurement science and measurement standards.
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Acoustics, Ultrasound and Vibration: Units
The quantity to be measured depends on the application.

  • Sound (acoustic) pressure is expressed in decibels (dB). The decibel is a dimensionless non-SI logarithmic unit that indicates the ratio of a physical quantity p relative to a specified reference level pref:
    Lp = 20 log10


    When expressing a quantity in decibels, it is important to state the magnitude of the reference level. In the case of microphones the reference level is 1 V/Pa; for hydrophones it is 1 V/µPa; and for the human ear it is 20 µPa.

  • Ultrasonic power is expressed in the SI unit watt (W).

  • Vibrations may be quantified differently depending on the type of instrument used to detect the vibrations. For example, the unit C/m s–2 is applied when a capacitive sensitive instrument is used, but other units may also be found.

Please see for:

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Acoustics, Ultrasound and Vibration
Committee structure
Strategic plan
International equivalence
Calibration and measurement capabilities (CMCs)
International comparisons
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BIPM contact person