SPL Distance Calculator
Calculate how sound pressure level drops as you move away from a speaker or source using the inverse square law, free in your browser.
Enter Values
How to use this calculator
- Enter the known SPL and distance, then the new distance.
- Read the SPL at the new distance.
How it works
Level change = 20 × log10(new distance ÷ old distance). Doubling distance drops 6 dB.
Worked example
100 dB at 1 m → 4 m. ≈ 88 dB (−12 dB).
Common mistakes
- Applying it indoors — reflections make real rooms differ from free-field.
- Using a line source (this assumes a point source).
Frequently asked questions
How does sound level change with distance?
By the inverse-square law, SPL drops about 6 dB each time the distance from a point source doubles.
Does 6 dB per doubling always hold?
It is for free-field point sources; rooms, reflections and line-array sources change the real-world fall-off.
Why 6 dB per doubling?
Sound energy spreads over a sphere; the inverse-square law gives a 6 dB drop each time distance doubles.
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Cite this tool
Zerdly. (2026). SPL Distance Calculator. Retrieved from https://www.zerdly.com/tools/spl-distance-calculator/
Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.