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

One hertz simply means "one (event) per second"; 100 Hz means "one hundred (events) 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. The reciprocal of frequency is time (period); a frequency of 1 Hz is equivalent to a period of 1 second, a frequency of 1 MHz to a period of 1 microsecond. In older writings, e.g. pre-WWII articles about radio transmissions and its electronics, the older but similar unit cycles per second (cps) is seen, along with related multiples kilocycles, megacycles, and so forth.

SI Multiples

1 kilohertzkHz103 Hz1 000 Hz
1 megahertzMHz106 Hz1 000 000 Hz
1 gigahertzGHz109 Hz1 000 000 000 Hz
1 terahertzTHz1012 Hz1 000 000 000 000 Hz
1 petahertzPHz1015 Hz1 000 000 000 000 000 Hz
1 exahertzEHz1018 Hz1 000 000 000 000 000 000 Hz


Hertz is also the name of the world's largest car rental company. See: The Hertz Corporation