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What is the quietest sound a human can hear?

0dBat the listener's ear

The threshold of human hearing is set at 0 dB, which corresponds to a sound pressure of 20 micropascals at 1 kHz. The National Park Service puts the lower threshold of hearing at 0 dB at 1 kHz, and the Federal Highway Administration defines the 20 µPa reference pressure as the threshold of human hearing.

Level
0 dBunweighted sound level
Daily limit
No daily limitNIOSH, at the loud end

What the numbers mean

How it was measured. Nominal threshold of human hearing at 1 kHz, defined as 0 dB sound pressure level (reference 20 µPa). Measured average thresholds are slightly higher (about 4 dB at 1 kHz according to HyperPhysics) and vary with frequency.

Every decibel figure for sound in air is a comparison with a reference pressure of 20 µPa, which the Federal Highway Administration describes as the threshold of human hearing. Zero decibels therefore does not mean silence; it means a sound exactly as strong as that reference. Quieter sounds, such as the inside of an anechoic chamber, get negative values.

The reference is a convenient round number rather than a precise average. HyperPhysics (Georgia State University) notes that the actual average threshold at 1000 Hz is closer to 4 decibels, and that the threshold varies with frequency: the ear is most sensitive in the low thousands of hertz and much less sensitive to deep bass.

The pressure involved is tiny. HyperPhysics notes that 0 dB represents a pressure change of less than one billionth of standard atmospheric pressure. CDC's chart of everyday sounds starts at 0 dB for the softest sound that can be heard, with normal breathing at 10 dB.

Is it safe?

Below 85 dBA, the level NIOSH allows for a full 8-hour day. (This figure is not A-weighted; treat it as a rough guide.) At this level, sound is not a hearing risk however long it lasts, though it can still disturb sleep or concentration.

Protecting your hearing

Not applicable. If you struggle to hear quiet sounds such as a ticking watch or whispering, a hearing test with an audiologist will show your own threshold at each frequency.

Earplug and earmuff ratings (NRR in the US, SNR in the UK and EU) are lab figures; real-world protection is usually lower. How to read the ratings.

Compared with sounds nearby

Using midpoints of each range. Energy multiplies by 10 every 10 dB; perceived loudness roughly doubles (why).

  • Air molecules (Brownian motion) (−24 to −23 dB): this has about 224× its sound energy and sounds about 5.1× as loud.
  • Normal breathing (10 dB): it has about 10× the sound energy of this and sounds about 2.0× as loud.
  • Ticking watch (20 dB): it has about 100× the sound energy of this and sounds about 4.0× as loud.

Questions

Does 0 dB mean silence?

No. 0 dB is a reference pressure of 20 µPa, roughly the faintest 1 kHz tone a person with good hearing can detect. Sounds quieter than that have negative decibel values.

Is everyone's threshold exactly 0 dB?

No. HyperPhysics notes that the measured average threshold at 1000 Hz is about 4 dB, and it varies between people and across frequencies.

Why 20 micropascals?

It is the agreed reference pressure for sound in air, chosen to sit near the limit of human hearing at 1 kHz, so most audible sounds come out as positive numbers.

Sources

  1. Understanding Sound - Natural Sounds, U.S. National Park Service. Supports: dB_low/dB_high: 0 dB at 1 kHz.The lower threshold of human hearing is 0 dB at 1kHz.Checked 2026-11-02.
  2. 2.0 Terminology - Construction Noise Handbook, Federal Highway Administration (US DOT). Supports: conditions: 20 µPa reference.the reference mean-square sound pressure of 20 µPa, the threshold of human hearingChecked 2026-11-02.
  3. Sound Intensity, HyperPhysics, Georgia State University. Supports: body: average threshold about 4 dB at 1000 Hz.or about 4 decibels, but zero decibels is a convenient referenceChecked 2026-11-02.
  4. Sound Intensity, HyperPhysics, Georgia State University. Supports: body: size of the pressure change.It represents a pressure change of less than one billionth of standard atmospheric pressureChecked 2026-11-02.
  5. What Noises Cause Hearing Loss? (archived copy, 31 Dec 2022), CDC National Center for Environmental Health. Supports: body: CDC chart starts at 0 dB.Softest sound that can be heard 0Checked 2026-11-02.

This page is general information, not medical advice. If you have ringing in your ears, muffled hearing or any change in your hearing, see an audiologist or your doctor.