Hz, rpm, and rad/s — the key frequency units
The hertz (Hz) is the SI unit of frequency and measures cycles per second; kilohertz (kHz), megahertz (MHz), and gigahertz (GHz) are its powers-of-ten multiples (×1,000, ×1,000,000, ×1,000,000,000). They describe audio (Hz/kHz), radio and broadcast (MHz), and Wi-Fi and processor clocks (GHz).
rpm and rad/s describe rotation rather than waves: rpm (revolutions per minute) is a rotational speed, where 60 rpm equals exactly 1 Hz (one revolution per second). rad/s is the angular frequency ω, with ω = 2πf, so 1 Hz equals 2π rad/s ≈ 6.283 rad/s. For more unit pairs, use our frequency conversion hub.