Hertz

The hertz (symbol: Hz, definition: 1/s) is a unit derived from time which measures frequency in the International System of Units (SI). Frequency is how often something happens. A frequency of 1 hertz means that something happens once a second. While hertz or Hz are the standard ways to express this unit, other expressions are sometimes used, as shown in the table.

Other ways to say hertz
inverse-seconds
cycles per second
cps

A sine wave with varying frequency

The note Middle C (the C in the middle of the piano) is 261.65 (262) Hz. This means there are 262 vibrations every second, which is heard as the note Middle C, when that piano key is played.

Humans are able to hear sounds between 20 and 20 000 Hz.^[1] Owls are able to hear sounds between 200 and 12000 Hz.^[2]

The basic unit is per second. The unit is named after the German physicist Heinrich Rudolf Hertz.

Multiple units

1000 hertz is 1 kilohertz. 1000 kilohertz is 1 megahertz, 1000 megahertz is 1 gigahertz: (see table)

Unit	Equal to:
Kilohertz (kHz)	1000 Hz
Megahertz (MHz)	1000 kHz
Gigahertz (GHz)	1000 MHz
Terahertz (THz)	1000 GHz
Petahertz (PHz)	1000 THz
Exahertz (EHz)	1000 PHz
Zettahertz (ZHz)	1000 EHz
Yottahertz (YHz)	1000 ZHz

Examples

• The frequency of the Earth's spinning (once per ~24 hours) is about 12 microhertz (much smaller than 1 Hz).
• The hertz is sometimes used to measure the power of a processor in computing and electronics.
• Amateur radio in the United States of America is at different frequencies between 1.8 and 1300 MHz^[3]
• Air traffic control uses frequencies between 3 and 25 MHz as well as frequencies between 108 and 136 MHz^[4]
• Musical note middle G (G4) has a frequency of 392 Hz.