The hertz (Hz) is the SI base unit of frequency, defined as one cycle per second, measuring how often a repeating event occurs. From AC power grid frequency (50 or 60 Hz) to audio tones and processor clock speeds, hertz is the universal language of frequency. One hertz equals exactly one cycle per second.

The kilohertz (kHz) equals 1,000 hertz, commonly used to describe audio frequencies, radio broadcasting bands, and early computer processor speeds. Human hearing ranges from about 20 Hz to 20 kHz, making this unit essential in audio engineering and music production. One kilohertz equals 1,000 cycles per second.