This calculator finds the difference between two deciBel (dB) values.

**Example Calculation**

Let’s say you have an RF attenuator with a value 30 dB followed by an amplifier with gain 20 dB.

- The total attenuation is
**30 dB – 20 dB = 10 dB** - The total amplification is
**20 dB – 30 dB = -10 dB**

**What does dB difference mean?**

The deciBel equivalent of a number X is given by **X _{dB} = 10*Log_{10}(X)**

Similarly the dB equivalent of a number Y is **Y _{dB} = 10*Log_{10}(Y)**

The dB equivalent of X/Y is **10*Log _{10}(X/Y)** =

**10*Log**–

_{10}(X)**10*Log**

_{10}(Y)**The difference between two dB numbers is equivalent to the Log of the ratio of the linear equivalent of the two.**

In the above example, the RF attenuator has a value of 30 dB which means it attenuates the signal by a factor of 1000. Alternatively, it amplifies the signal by -30 dB = (1/1000).

The RF amplifier has a value of 20 dB which means that it amplifies the signal 100 times.

To calculate the effective gain we calculate the product of the two numbers: (1/1000)*100 = 1/10.

The Logarithm of 1/10 is 10*Log_{10}(1/10) = -10 dB which represents the total or cascaded gain.

The same number was found by adding the gain numbers in dB: **20 dB – 30 dB = -10 dB**

**Table of dB Difference vs Linear**

This table provides the dB difference between two numbers and the ratio of the linear equivalent

dB Difference | Linear Ratio |
---|---|

100 | 10000000000 |

90 | 1000000000 |

80 | 100000000 |

70 | 10000000 |

60 | 1000000 |

50 | 100000 |

40 | 10000 |

30 | 1000 |

20 | 100 |

10 | 10 |

0 | 1 |

-10 | 0.1 |

-20 | 0.01 |

-30 | 0.001 |

-40 | 0.0001 |

-50 | 0.00001 |

-60 | 0.000001 |

-70 | 0.0000001 |

-80 | 0.00000001 |

-90 | 0.000000001 |

-100 | 0.0000000001 |

**Related Calculators**

- dBm Addition – Add two power values in
**dBm**doesn’t follow the same rules as adding two dB values - dB Addition – follows the same rules as subtraction