What Is Hz (Hertz)?
Hertz measures how many times per second a sound wave vibrates. Learn what Hz means for tone generators, speakers, and hearing.
Last updated: September 17, 2025
Hertz (Hz) is the unit of frequency. One hertz equals one complete vibration cycle per second. When a speaker plays a 440 Hz tone, the diaphragm moves back and forth 440 times every second.
Why Hz matters for audio tools
Tone generators, tuners, and hearing tests all work in hertz. The audible range for most humans spans roughly 20 Hz to 20,000 Hz (20 kHz), though sensitivity drops at the extremes and with age. Lower Hz values sound like rumble or bass; higher values sound like treble or hiss.
Common reference frequencies
| Frequency | Typical use |
|---|---|
| 60 Hz | North American AC mains hum |
| 50 Hz | European AC mains hum |
| 440 Hz | Concert pitch (A4) |
| 1,000 Hz | Standard audio test tone |
| 8,000–15,000 Hz | Treble and hearing limit checks |
Hz vs musical notes
Musical notes map to specific frequencies under equal temperament. A4 is defined as 440 Hz in modern Western tuning. Use our Hz to Note converter to translate between frequency and note names.
How to test a specific Hz
Open any fixed-frequency page (for example 440 Hz or 1 kHz) and tap Play. Start at low volume. For arbitrary frequencies, use the tone generator and set the slider to your target Hz.
Frequently asked questions
What is the difference between Hz and dB?
Hz measures frequency (pitch). Decibels (dB) measure sound pressure level (loudness). A 1,000 Hz tone can be quiet or loud depending on volume.
Can everyone hear 20 Hz?
Most adults cannot perceive 20 Hz as a distinct pitch — it feels more like vibration. Subwoofers and large speakers are needed to reproduce very low frequencies.
Is higher Hz always “higher pitch”?
Yes. Doubling the frequency raises the pitch by one octave. 880 Hz sounds one octave above 440 Hz.