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Why are underwater decibels different from air decibels?

26–61.5dB re 1 µPanot applicable

Underwater sound levels are quoted in dB re 1 µPa, while in-air levels use 20 µPa, which alone adds 26 dB to underwater figures. Because water is much denser and carries sound faster, a sound wave of the same intensity reads 61.5 dB higher in water than in air, according to DOSITS (University of Rhode Island). So 236 dB underwater is nothing like 236 dB in air.

Level
26–61.5 dB re 1 µPadecibels relative to 1 micropascal, measured in water
Daily limit
Underwater levelnot an air level

What the numbers mean

How it was measured. Not a sound. These are correction terms from DOSITS: 26 dB comes from the different reference pressures (1 µPa in water, 20 µPa in air); the full 61.5 dB also accounts for water's much higher density and sound speed. Subtract 61.5 dB from an underwater level to get the in-air level of a sound wave with the same intensity.

Decibels are ratios against a reference, and acousticians use different references in the two media. DOSITS explains that underwater sound is referenced to a pressure of 1 microPascal (µPa), while sound in air is referenced to 20 µPa, chosen because it matches the hearing threshold of young adults at their most sensitive frequencies. That difference in reference pressures accounts for 26 dB.

The second reason is the medium itself. The intensity of a sound wave depends on the pressure and on the density and sound speed of the medium; for the same pressure, higher density and higher sound speed both give a lower intensity. Water is far denser than air and sound travels much faster in it, which accounts for a further 35.5 dB. Together, sound waves of equal intensity in watts per square metre differ by 61.5 dB in relative level, and DOSITS says this amount must be subtracted from underwater levels to get the in-air level of equal intensity. Guinness World Records cites the same 61.5 dB difference.

Even after the correction, comparisons are rough, because underwater figures are usually source levels back-calculated to 1 m from the animal or machine, while in-air figures are usually measured at a listener's position. The safest habit is to always state the reference: "dB re 1 µPa" for water and "dB re 20 µPa" for air.

Is it dangerous?

Measured in water against a 1 µPa reference, so the number cannot be compared directly with levels in air. See the underwater note on the Scroll. Marine-mammal and diver exposure criteria use their own metrics and are outside the scope of this page.

Protecting your hearing

Not applicable: this is a unit conversion. For divers, the practical point is that underwater dB figures for sonar or airguns cannot be judged by in-air hearing rules.

Questions

Is 200 dB underwater the same as 200 dB in air?

No. Underwater levels use a 1 µPa reference instead of 20 µPa (26 dB difference), and water's density and sound speed add a further 35.5 dB, for 61.5 dB in total at equal intensity.

How do I convert underwater dB to air dB?

DOSITS says to subtract 61.5 dB from a level in dB re 1 µPa to get the in-air level (re 20 µPa) of a sound with the same intensity.

Sources

  1. How does sound in air differ from sound in water?, DOSITS, University of Rhode Island (Wayback Machine copy). Supports: dB_low: 26 dB reference-pressure term.The difference in reference pressures causes 26 dB of the 61.5 dB differenceChecked 2026-11-02.
  2. How does sound in air differ from sound in water?, DOSITS, University of Rhode Island (Wayback Machine copy). Supports: dB_high: 61.5 dB total.The result is that sound waves with the same intensities in water and air when measured in watts per square meter have relative intensities that differ by 61.5 dBChecked 2026-11-02.
  3. How does sound in air differ from sound in water?, DOSITS, University of Rhode Island (Wayback Machine copy). Supports: 35.5 dB from density and sound speed.The differences in densities and sound speeds account for the other 35.5 dBChecked 2026-11-02.
  4. How does sound in air differ from sound in water?, DOSITS, University of Rhode Island (Wayback Machine copy). Supports: 1 µPa reference in water.Scientists have arbitrarily agreed to use as the reference intensity for underwater sound the intensity of a sound wave with a pressure of 1 microPascal (μPa)Checked 2026-11-02.
  5. How does sound in air differ from sound in water?, DOSITS, University of Rhode Island (Wayback Machine copy). Supports: 20 µPa reference in air.scientists have agreed to use as the reference intensity for sound in air the intensity of a sound wave with a pressure of 20 microPascals (μPa)Checked 2026-11-02.
  6. How does sound in air differ from sound in water?, DOSITS, University of Rhode Island (Wayback Machine copy). Supports: Why the medium matters.For the same pressure, higher density and higher sound speed both give a lower intensityChecked 2026-11-02.
  7. Loudest animal sound, Guinness World Records. Supports: Independent statement of 61.5 dB.there is a difference of some 61.5 dB between a sound passing through air or waterChecked 2026-11-02.
  8. What are common underwater sounds?, DOSITS, University of Rhode Island (Wayback Machine copy). Supports: Underwater figures are source levels at 1 m.Source levels are defined as if the receiver was one meter from the sound sourceChecked 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.