By Zencalcy Editorial TeamLast reviewed About us
Sound pressure level is the decibel form of the root-mean-square pressure variation a microphone measures. It uses a reference of 20 µPa, close to the quietest tone a young ear can detect at 1 kHz. Most sound level meters and noise regulations are written in dB SPL.
Convert acoustic pressure to dB SPL and back.
L_p = 20 log₁₀(p / p₀)
p is the RMS sound pressure and p₀ = 20 µPa. The 20 multiplier comes from pressure amplitude rather than power.
| Symbol | Meaning |
|---|---|
| L_p | Sound pressure level in dB SPL. |
| p | RMS sound pressure in pascals. |
| p₀ | Reference pressure, 20 µPa. |
20 log₁₀(0.2 / 0.00002) = 20 log₁₀(10,000) = 80 dB SPL. That is roughly the level of a loud conversation or a busy street.
Continue with the Speed of Sound Calculator, String Harmonics Calculator, or the Sound Wavelength Calculator — or browse more acoustics and sound tools and all physics calculators.
Standard SPL uses RMS pressure with a stated time weighting, such as fast or slow. Peak levels are quoted separately for impulse noise and are usually several decibels higher.
Results are computed from the standard equations of classical mechanics. Unit conversions use the SI definitions published by NIST. Air resistance is ignored unless the calculator names a drag model.
Reference material used to build and check this calculator:
Last reviewed: September 2026. See how we build and check every tool on the about page.
Free calculator · No signup
Free calculator · No signup
Free calculator · No signup
Free calculator · No signup
Free calculator · No signup
Free calculator · No signup
Content updated: September 2026