分贝（decibel）是量度两个相同单位之数量比例的单位，主要用于度量声音强度，常用dB表示。「分」（deci-）指十分之一，个位是「贝」或「贝尔」（bel，纪念发明家亚历山大·贝尔），但一般只用分贝。

常用的空气参考声压为 = 20 µPa（微帕斯卡）（rms），它通常被认为是人类的最少听觉响应值（大约是3米以外飞行的蚊子声音）。最完善的水平测量，测量1帕斯卡等于94分贝声压级。在其他介质，如水下，1微帕斯卡更为普遍。这些标准被ANSIS1.1-1994.所收录。

The decibel (dB) is a logarithmic unit used to express the ratio of two values of a physical quantity, often power or intensity. One of these values is often a standard reference value, in which case the decibel is used to express the level of the other value relative to this reference. The number of decibels is ten times the logarithm to base 10 of the ratio of two power quantities, or of the ratio of the squares of two field amplitude quantities. One decibel is one tenth of one bel, named in honor of Alexander Graham Bell; however, the bel is seldom used.