By Zencalcy Editorial TeamLast reviewed About us
Sound intensity level expresses intensity on a logarithmic scale relative to 10⁻¹² W/m², roughly the threshold of hearing at 1 kHz. A tenfold increase in intensity adds 10 dB, and a doubling adds about 3 dB. The scale compresses the enormous range the ear can handle into a manageable set of numbers.
Decibels from acoustic intensity, and the inverse.
L = 10 log₁₀(I / I₀)
I₀ is 10⁻¹² W/m². The 10 multiplier applies because intensity is proportional to the square of pressure; pressure levels use 20.
| Symbol | Meaning |
|---|---|
| L | Sound intensity level in dB. |
| I | Sound intensity in W/m². |
| I₀ | Reference intensity, 10⁻¹² W/m². |
10 log₁₀(10⁻⁵ / 10⁻¹²) = 10 log₁₀(10⁷) = 70 dB. That is a typical level for a busy office or a normal conversation at close range.
Continue with the Sound Power Level Calculator, Sound Pressure Level Calculator, or the Speed of Sound Calculator — or browse more acoustics and sound tools and all physics calculators.
Intensity spans more than a trillion-fold between the hearing threshold and pain. A logarithmic ratio compresses that range, and the reference fixes the zero point at 10⁻¹² W/m².
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.
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Content updated: September 2026