The **hertz** (symbol **Hz**, named in honor of the 19th-century German physicist Heinrich Rudolf Hertz) is the derived unit of frequency in the International System of Units (SI) and is defined as one cycle per second.

\[1\;\textrm{Hz}=\dfrac{1}{s}\]

Given any phenomenon consisting of an event that repeats itself periodically, the frequency of this phenomenon is defined as the number of repetitions of the event in a certain time interval. Assuming that this time interval is equal to 1 second, the number of repetitions of the event in one second is measured in Hz. For example, if an event periodically repeats itself 10 times per second, we will say that such an event has a frequency equal to 10 Hz.

## Multiples

Below are reported all the multiples and submultiples of Hz adopted in the International System. In addition to the symbol and the full value expressed in hertz, for each multiple and submultiple we have also indicated the value expressed in scientific notation.

Multiple | Name | Symbol | Submultiple | Name | Symbol |
---|---|---|---|---|---|

10^{0} | hertz | Hz | |||

10^{1} | decahertz | daHz | 10^{–1} | decihertz | dHz |

10^{2} | hectohertz | hHz | 10^{–2} | centihertz | cHz |

10^{3} | kilohertz | kHz | 10^{–3} | millihertz | mHz |

10^{6} | megahertz | MHz | 10^{–6} | microhertz | µHz |

10^{9} | gigahertz | GHz | 10^{–9} | nanohertz | nHz |

10^{12} | terahertz | THz | 10^{–12} | picohertz | pHz |

10^{15} | petahertz | PHz | 10^{–15} | femtohertz | fHz |

10^{18} | exahertz | EHz | 10^{–18} | attohertz | aHz |

10^{21} | zettahertz | ZHz | 10^{–21} | zeptohertz | zHz |

10^{24} | yottahertz | YHz | 10^{–24} | yoctohertz | yHz |