The hertz (symbol: Hz) is the SI unit of frequency. It is named in honor of the German physicist Heinrich Rudolf Hertz who made important scientific contributions to electromagnetism.

## Definition

One hertz is defined as one cycle per second.

1 Hz = 1 s−1

## SI multiples

Multiple Name Symbol Multiple Name Symbol
100 hertz Hz
101 decahertz daHz 10−1 decihertz dHz
102 hectohertz hHz 10−2 centihertz cHz
103 kilohertz kHz 10−3 millihertz mHz
106 megahertz MHz 10−6 microhertz µHz
109 gigahertz GHz 10−9 nanohertz nHz
1012 terahertz THz 10−12 picohertz pHz
1015 petahertz PHz 10−15 femtohertz fHz
1018 exahertz EHz 10−18 attohertz aHz
1021 zettahertz ZHz 10−21 zeptohertz zHz
1024 yottahertz YHz 10−24 yoctohertz yHz

## Explanation

One hertz simply means "one per second" (1 / s); 100 Hz means "one hundred per second", and so on. The unit may be applied to any periodic event – for example, a clock might be said to tick at 1 Hz, or a human heart might be said to beat at 1.2 Hz. Frequency of random events, such as radioactive decays, is expressed in becquerels.

The name hertz was adopted by the CGPM (Conférence générale des poids et mesures) in 1960, replacing the previous name for the unit, cycles per second (cps), along with its related multiples, primarily kilocycles (kc) and megacycles (mc). Hertz largely replaced cycles in common use by 1970.