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hertz | |
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General information | |

Unit system | SI |

Unit of | frequency |

Symbol | Hz |

Named after | Heinrich Hertz |

In SI base units | s^{−1} |

The **hertz** (symbol: **Hz**) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second.^{[1]}^{[3]} The hertz is an SI derived unit whose expression in terms of SI base units is s^{−1}, meaning that one hertz is the reciprocal of one second.^{[2]} It is named after Heinrich Rudolf Hertz (1857–1894), the first person to provide conclusive proof of the existence of electromagnetic waves. Hertz are commonly expressed in multiples: kilohertz (kHz), megahertz (MHz), gigahertz (GHz), terahertz (THz).

Some of the unit's most common uses are in the description of periodic waveforms and musical tones, particularly those used in radio- and audio-related applications. It is also used to describe the clock speeds at which computers and other electronics are driven. The units are sometimes also used as a representation of the energy of a photon, via the Planck relation *E* = *hν*, where *E* is the photon's energy, *ν* is its frequency, and *h* is the Planck constant.

**^**"hertz". (1992).*American Heritage Dictionary of the English Language*(3rd ed.), Boston: Houghton Mifflin.- ^
^{a}^{b}"SI Brochure: The International System of Units (SI) – 9th edition" (PDF).*BIPM*: 26. Retrieved 7 August 2022. **^**Although hertz is equivalent to cycle per second (cps), the SI explicitly states that "cycle" and "cps" are not units in the SI, likely due to ambiguity in the terms.^{[2]}