Hertz

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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 per second"; 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.

In older writings, the equivalent unit cycle per second (cps) is seen.

SI Multiples

1 kilohertz (symbol kHz) = 10³ Hz = 1,000 Hz

1 megahertz (symbol MHz) = 10⁶ Hz = 1,000,000 Hz

1 gigahertz (symbol GHz) = 10⁹ Hz = 1,000,000,000 Hz

1 terahertz (symbol THz) = 10¹² Hz = 1,000,000,000,000 Hz

1 petahertz (symbol PHz) = 10¹⁵ Hz = 1,000,000,000,000,000 Hz

1 exahertz (symbol EHz) = 10¹⁸ Hz = 1,000,000,000,000,000,000 Hz

Examples

• 50 or 60 Hz, electromagnetic – standard AC electric power supplies
• 261.625 Hz, acoustic – the musical note middle C
• 440 Hz, acoustic – concert pitch (A above middle C), used for tuning musical instruments
• 104 kHz, transitions – the clock speed of the first commercially produced microprocessor, the Intel 4004 (1971)
• 1 to 8 MHz, transitions – clock speeds of early home/personal computers (late 1970s, early-to-mid 1980s)
• 88 to 108 MHz, electromagnetic – FM radio broadcasts
• 2.2 GHz, transitions – clock speed of the Pentium 4 microprocessor (2002)
• 460 THz, electromagnetic – red light
• 30 PHz, electromagnetic – x-rays