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Hertz (Hz) ○◂｜Definition｜1st｜20251119205401-00-⌔
Hertz
The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), often described as being equivalent to one event (or cycle) per second.12 The hertz is an SI derived unit whose formal expression in terms of SI base units is 1/s or s, meaning that one hertz is one per second or the reciprocal of one second.3 It is used only in the case of periodic events. It is named after Heinrich Rudolf Hertz (1857–1894), the first person to provide conclusive proof of the existence of electromagnetic waves. For high frequencies, the unit is 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.
Printed 2026-06-28.
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Link to original Footnotes
“hertz”. (1992). American Heritage Dictionary of the English Language (3rd ed.), Boston: Houghton Mifflin. ↩
Although hertz is often said to imply 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. ↩
“SI Brochure: The International System of Units (SI) – 9th edition” (PDF). BIPM. p. 26. Retrieved 7 August 2022. ↩
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