What Is a Hertz?
The complete guide to hertz, the SI unit of frequency, covering sound, radio, and computing.
Last updated: 2026-03-15
Definition
A hertz (symbol: Hz) is the SI unit of frequency. It measures the number of complete cycles of a periodic event per second:
1 Hz = 1 cycle per second = 1 s-1
Frequency Examples
| Phenomenon | Frequency |
|---|---|
| Earth's rotation | 0.0000116 Hz (once per day) |
| Human heartbeat | 1-2 Hz (60-120 bpm) |
| Power grid (US) | 60 Hz |
| Power grid (Europe) | 50 Hz |
| Bass guitar lowest note | 41 Hz |
| Middle C (piano) | 261.63 Hz |
| Concert A (tuning) | 440 Hz |
| AM radio | 540-1,600 kHz |
| FM radio | 87.5-108 MHz |
| WiFi (2.4 GHz band) | 2.4 GHz |
| WiFi (5 GHz band) | 5 GHz |
| CPU clock speed | 2-5 GHz |
Hertz Multiples
| Unit | Value | Common Use |
|---|---|---|
| Millihertz (mHz) | 0.001 Hz | Geological movements |
| Hertz (Hz) | 1 Hz | Sound, vibrations |
| Kilohertz (kHz) | 1,000 Hz | Audio, AM radio |
| Megahertz (MHz) | 106 Hz | FM radio, old CPUs |
| Gigahertz (GHz) | 109 Hz | WiFi, modern CPUs |
| Terahertz (THz) | 1012 Hz | Infrared spectroscopy |
History
The hertz is named after Heinrich Rudolf Hertz (1857-1894), a German physicist who was the first to conclusively prove the existence of electromagnetic waves predicted by James Clerk Maxwell. The unit was adopted by the CGPM in 1960, replacing "cycles per second" (cps).
Applications
Display Technology
Monitor refresh rates (60 Hz, 120 Hz, 144 Hz, 240 Hz) determine how smoothly motion appears on screen. Higher Hz means smoother visuals, especially important for gaming and video editing.
Music and Sound
Musical pitch is measured in hertz. Standard tuning uses A4 = 440 Hz. Doubling the frequency raises the pitch by one octave (A5 = 880 Hz).
Convert frequencies with our frequency converter.