Sound Intensity Calculator

Work out sound intensity instantly with clear inputs, formula shown and shareable results.

About Sound Intensity Calculator

Sound from a point source spreads over a sphere, so intensity is power divided by 4 pi r^2. A 50 mW source at 3 m gives 4.4e-4 W/m2, about 86 dB. Doubling the distance quarters the intensity, which is the 6 dB per doubling rule used in noise assessment.

Formulas

Intensity from power

I = P / (4 pi r^2)

Level

L = 10 log10(I / 1e-12)

Worked example

With the default values below, Sound Intensity Calculator returns Sound Intensity of 4.42097 × 10⁻⁴. Change any input above and every figure here is recalculated in your browser.

Inputs used

Acoustic power of the sourceminimum 0 W: 0.05 W
Distance from the sourceminimum 0 m: 3 m

Results

Sound Intensity: 4.42097 × 10⁻⁴ W/m2
Equivalent Sound Level: 86.46 dB
Area Of The Wavefront Sphere: 113.0973 m2
Same Intensity In mW/m2: 0.44210

Step by step

1Values used
2Intensity from power
3Level
4Sound Intensity= 0.00044 W/m2
5Equivalent Sound Level= 86.46 dB
6Area Of The Wavefront Sphere= 113.0973 m2
7Same Intensity In mW/m2= 0.44210

Assumptions and limits

The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 5 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why 1e-12 W/m2 as the reference?

It is the nominal threshold of human hearing at 1 kHz, so 0 dB marks the quietest audible sound.

Does this apply indoors?

Only close to the source. Room reflections build a reverberant field that stops the inverse square law from applying beyond the critical distance.