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.

Revolutions per minute (rpm) measures rotational speed, expressing how many complete turns an object makes in one minute. It is the most common unit for engine speed, hard drive spin rates, and power tool specifications worldwide. One rpm equals exactly 1/60 hertz or approximately 0.01667 Hz.