FREQUENCY UNITS

Audible acoustic waves repeat at intervals that are only a small fraction of a second. The lowest sound frequency a human being can hear is about 20 cycles per second, or 20 hertz (20 Hz). The highest frequency an acoustic wave can have and still be heard by a person with keen ears is a thousand times higher: 20,000 Hz.
Radio waves travel in a different medium than sound waves. Their lowest frequency is a few thousand hertz, and their highest frequencies range into the trillions of hertz. Infrared (IR) and visible-light waves occur at frequencies much higher than radio waves. Ultraviolet (UV) waves, x-rays, and gamma () rays range into quadrillions and quintillions of hertz, vibrating more than 1 trillion times faster than middle C on the musical scale.
To denote high frequencies, scientists and engineers use frequency units of kilohertz (kHz), megahertz (MHz), gigahertz (GHz), and terahertz (THz). Each unit is a thousand times higher than the previous one in this succession. That is, 1 kHz = 1,000 Hz, 1 MHz = 1,000 kHz, 1 GHz =1,000 MHz, and 1 THz = 1,000 GHz.