Hertz (Hz)

Hertz (Hz) is the SI unit of frequency — one cycle per second. Named after the German physicist Heinrich Hertz, who proved the existence of electromagnetic waves in 1887.

Common multiples and where you encounter them:

• Hz — seismic and infrasound (under 20 Hz, below human hearing)
• kHz (10³ Hz) — audio range (20 Hz to 20 kHz); AM radio
• MHz (10⁶ Hz) — FM radio (88-108 MHz); CPU clocks before 2000
• GHz (10⁹ Hz) — Wi-Fi, modern CPUs, microwave ovens (2.45 GHz)
• THz (10¹² Hz) — infrared, terahertz imaging
• PHz (10¹⁵ Hz) — visible light

Refresh rates for displays are quoted in Hz: standard LCD 60 Hz, gaming displays 120/144/240 Hz. Higher refresh rates reduce motion blur and input lag. The threshold where humans stop perceiving improvement varies but typically falls between 90 and 120 Hz for most viewers.