Sound Level by Distance Calculator
Estimate a sound level at another distance under the ideal free-field inverse-square spreading assumption for a point source.
How to use this calculator
- Enter known sound level and both distances in metres.
- Confirm that all inputs use the stated units and the same population, period or scope.
- Change one assumption at a time when comparing scenarios.
Formula used by the sound level distance calculator
L₂ = L₁ − 20 log₁₀(r₂/r₁)
- L₂ = L₁ − 20 log₁₀(r₂/r₁)
- Reflections, barriers, source directivity, absorption and background noise are not included.
- Inputs are validated against required ranges and outputs are rounded for readability.
Worked examples
Worked example
80 dB at 2 m, estimated at 8 m.
The ideal distance-only estimate decreases by about 12.04 dB.
The ideal distance-only estimate decreases by about 12.04 dB.
Understanding the result
Estimate a sound level at another distance under the ideal free-field inverse-square spreading assumption for a point source.
Reflections, barriers, source directivity, absorption and background noise are not included.
Important notes
Reflections, barriers, source directivity, absorption and background noise are not included.
Use the result as a calculation aid for the inputs supplied; confirm critical specifications independently.
Frequently asked questions
Why does level drop with distance?
Sound energy spreads over a larger area in a free field, reducing intensity with distance.
Does this model a real room?
No; room reflections and absorption can change the relationship.
How do I use this calculator?
Enter known sound level and both distances in metres.
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Related explanations
Learn the method behind the number or compare the terminology before using the calculator.
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This page provides a calculation tool plus explanatory information so you can understand what the result means and when the underlying method may not fit your situation.