Alternative Title:

**dB**.**Decibel**(**dB**), unit for expressing the ratio between two physical quantities, usually amounts of acoustic or electric power, or for measuring the relative loudness of sounds.**One decibel**(0.1 bel) equals 10 times the common logarithm of the power ratio.How loud is 20 decibels?

Comparitive Examples of Noise Levels

Noise Source | Decibel Level | Decibel Effect |
---|---|---|

Library, bird calls (44 dB); lowest limit of urban ambient sound | 40 | One-eighth as loud as 70 dB. |

Quiet rural area. | 30 | One-sixteenth as loud as 70 dB. Very Quiet. |

Whisper, rustling leaves | 20 | |

Breathing | 10 | Barely audible |

What is the formula for dB?

The base-10

**logarithm**of the ratio of the two power quantities is the number of bels. The number of decibels is ten times the number of bels (equivalently, a decibel is one-tenth of a bel). P and P_{0}must measure the same type of quantity, and have the same units before calculating the ratio.