By Zencalcy Editorial TeamLast reviewed About us
Sound intensity is acoustic power crossing a unit area. A point source radiating uniformly spreads its power over a sphere of area 4πr², so intensity falls with the square of distance. It is a physical quantity in watts per square metre, distinct from the logarithmic sound intensity level.
Acoustic power per unit area from a point source.
I = P / (4 π r²)
P is the radiated acoustic power and r the distance in a free field. Real sources are directional, so a directivity factor would multiply the right side for on-axis estimates.
| Symbol | Meaning |
|---|---|
| I | Sound intensity. |
| P | Acoustic power of the source. |
| r | Distance from the source. |
I = 1 / (4π × 2²) = 0.0199 W/m², which is 103 dB relative to 10⁻¹² W/m². Doubling the distance drops the level by 6 dB.
Continue with the Sound Intensity Level Calculator, Sound Power Level Calculator, or the Sound Pressure Level Calculator — or browse more acoustics and sound tools and all physics calculators.
No. Loudness is a perceptual quantity that also depends on frequency and duration. Intensity is the physical power per area, and two sounds with equal intensity can seem very different in loudness.
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.
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Content updated: September 2026