By Zencalcy Editorial TeamLast reviewed About us
Sound power level describes how much acoustic energy a source emits, independent of where you stand. It is the right figure for comparing machines or loudspeakers, while sound pressure level depends on distance and room. The reference power is 1 picowatt, 10⁻¹² W.
Decibels of acoustic power relative to 1 pW.
L_W = 10 log₁₀(P / P₀)
P is radiated acoustic power and P₀ = 10⁻¹² W. Sound power level is a property of the source; sound pressure level at a listener also depends on distance and the room.
| Symbol | Meaning |
|---|---|
| L_W | Sound power level in dB SWL. |
| P | Acoustic power in watts. |
| P₀ | Reference power, 10⁻¹² W. |
10 log₁₀(0.001 / 10⁻¹²) = 90 dB SWL. A small loudspeaker might radiate 1 W, which is 120 dB SWL, while a whisper is around 10⁻⁹ W, or 30 dB SWL.
Continue with the Sound Pressure Level Calculator, Speed of Sound Calculator, or the String Harmonics Calculator — or browse more acoustics and sound tools and all physics calculators.
SWL is the total power a source radiates. SPL is the pressure at a particular place, so it falls with distance and changes with reflections. One source has a single SWL but many possible SPL readings.
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