Sound Pressure Level Converter
Sound pressure level (SPL) is the decibel measure used by sound level meters, hearing standards, and noise regulations. It relates to physical sound pressure through a logarithm referenced to 20 micropascals in air. Enter either an SPL in decibels or a sound pressure, choose the units, and the converter moves between them using the standard definition. You can also adjust the reference pressure for underwater or other media.
Sound pressure level formula
SPL (dB) = 20 * log10(p / p_ref)
p = p_ref * 10^(SPL / 20)
p_ref (air) = 20 uPa = 0.00002 Pa
The result for dB to pressure is shown in the pressure unit you select; the result for pressure to dB is in decibels relative to the reference you enter.
Worked example
An SPL of 94 dB with the air reference gives p = 0.00002 * 10^(94/20) = 0.00002 * 50,118.7 which is about 1.00 Pa. This is the standard 94 dB calibration level for sound level meters.
Sound pressure level: frequently asked questions
What is sound pressure level?
Sound pressure level (SPL) expresses sound pressure on a logarithmic decibel scale relative to a reference pressure. In air the reference is 20 micropascals, the nominal threshold of human hearing. SPL in decibels equals 20 times the base-10 logarithm of the pressure divided by the reference.
Why is the reference pressure 20 micropascals?
20 micropascals (2 times 10 to the power minus 5 pascals) is the internationally agreed reference for airborne sound, chosen to approximate the quietest sound a healthy young ear can detect at 1 kilohertz. This converter uses that reference, so 0 decibels corresponds to 20 micropascals.
How do I convert decibels back to pascals?
Pressure equals the reference pressure times 10 raised to the SPL divided by 20. For example 94 decibels gives 20e-6 times 10 to the power 4.7, which is about 1 pascal, the standard calibration level for sound level meters.
Does a 6 decibel change really double the pressure?
Yes. Because the scale uses 20 times a base-10 logarithm, every increase of about 6.02 decibels doubles the sound pressure, and every 20 decibels multiplies it by ten. A 10 decibel rise corresponds to about a 3.16 times increase in pressure.
Official sources
- NIST, acoustics and decibel reference: nist.gov.
- Standard SPL definition with reference 20 micropascals (ISO 1683 convention).
Reviewed by the CalculatorHub team, edited by James Graham, 19 June 2026. See our methodology.