How this calculator works
Choose the quantity before entering its level or physical value. Pressure uses an RMS amplitude ratio, whereas intensity uses a power-per-area ratio. The default references are 20 micropascals and 10^-12 W/m2 for airborne sound. Sound-power mode assumes uniform radiation over a sphere in a free field. The pressure and intensity references do not by themselves specify a material impedance.
Formula
Lp = 20 log10(prms/pref). LI = 10 log10(I/Iref). An isotropic point source gives I = P/(4 pi r²). Inverse: p = pref 10^(Lp/20), I = Iref 10^(LI/10).
Worked example
An RMS pressure of 0.02 Pa is 1000 times 20 micropascals and gives 60 dB SPL. Intensity of 10^-10 W/m2 is 100 times the reference and gives 20 dB.
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Frequently asked questions
Can a decibel level be negative?
Yes. A negative level means the positive quantity is below its reference.
Is sound intensity measured in watts?
Intensity is watts per square metre. Watts alone measure total acoustic power.
Is this dBA?
No. A-weighting depends on the sound spectrum and frequency response, which are not included here.