Sound Intensity Level Calculator
Sound intensity level (SIL) converts a physical sound intensity in watts per square metre into the familiar decibel scale. The formula is SIL = 10 log10(I / I0), where I0 = 10^-12 W/m^2 is the internationally agreed reference threshold of hearing. A whisper at 1 m sits around 30 dB; conversation around 60 dB; a rock concert in front of the speakers can reach 110 dB or more. Because the scale is logarithmic, each 10 dB increase represents a tenfold rise in physical intensity. Enter the intensity in W/m^2 and the calculator returns the level in dB instantly.
Sound intensity level formula
SIL (dB) = 10 × log10(I / I0)
Where I is the measured intensity in W/m^2 and I0 = 10^-12 W/m^2 is the reference intensity. The factor of 10 converts bels to decibels.
Common sound levels for reference
- Threshold of hearing: 10^-12 W/m^2 = 0 dB
- Rustling leaves: 10^-11 W/m^2 = 10 dB
- Whisper at 1 m: 10^-9 W/m^2 = 30 dB
- Normal conversation at 1 m: 10^-6 W/m^2 = 60 dB
- Heavy traffic: 10^-4 W/m^2 = 80 dB
- OSHA 8-hr exposure limit: 90 dB
- Jet engine at 100 m: 10 W/m^2 = 130 dB (pain threshold)
Frequently asked questions
What is sound intensity level?
Sound intensity level (SIL) is the logarithmic ratio of sound intensity I to the reference intensity I0 = 10^-12 W/m^2, expressed in decibels: SIL = 10 log10(I/I0). It describes how loud a sound is on the decibel scale.
What is the reference intensity I0?
The reference intensity I0 is 10^-12 W/m^2 (one picowatt per square metre). This value corresponds roughly to the threshold of human hearing at 1 kHz and is the internationally agreed reference for decibel calculations.
Why does doubling the intensity add only 3 dB?
Because the scale is logarithmic. Doubling I gives 10 log10(2) approximately 3.01 dB more. To increase level by 10 dB you need to multiply intensity by 10; by 20 dB you need 100 times the intensity.
What is a typical sound intensity level for conversation?
Normal conversation at about 1 m is roughly 10^-6 W/m^2, which equals 60 dB. A jet engine at close range can reach 1 W/m^2, or 120 dB.
What is the difference between sound intensity and sound pressure level?
Sound intensity is power per unit area (W/m^2); sound pressure level (SPL) is based on pressure. For a free-field plane wave in air they are numerically equal in decibels at the standard references, but the two quantities are fundamentally different physical measures.
Official sources
- NIST: Acoustics and vibration calibration.
- OSHA: Noise and Hearing Conservation.
- OpenStax University Physics Vol. 1, Chapter 17: Sound.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.