Sound Level vs Distance Calculator (Inverse Square Law)
Enter a sound level measured at one distance and a new distance.
Your numbers
Your results
Sound level at the new distance (dB)
Sound level at the new distance (dB)
—
Drop (dB)
—
Distance for the target level (m)
—
Intensity ratio
—
Sound Level vs Distance Calculator (Inverse Square Law) by TheCalcTools
How the Sound Level vs Distance Calculator (Inverse Square Law) works
Outdoors, sound from a small source spreads over a sphere, so intensity falls with the square of distance. In decibels that is a 6 dB drop each time the distance doubles: L₂ = L₁ − 20 log₁₀(r₂/r₁).
Indoors, reflections keep levels higher than this; ground, air absorption and barriers reduce them further outdoors.
The formula
L₂ = L₁ − 20 log₁₀(r₂ ÷ r₁)
Worked example
Using the default values shown in the calculator:
| Sound level at the first distance (dB) | 100 |
|---|---|
| First distance (m) | 1 |
| New distance (m) | 10 |
| Target level (dB, optional) | 70 |
- 100 dB at 1 m drops to 80.0 dB at 10 m.
- To reach 70 dB, move to 31.62 m.
Result:
| Sound level at the new distance (dB) | 80.0 |
|---|---|
| Drop (dB) | 20.0 |
| Distance for the target level (m) | 31.62 |
| Intensity ratio | 1 : 100 |
Frequently asked questions
How far away is 100 dB at 1 m quiet enough?
To reach 70 dB in free field you need about 31.6 m.
Sources and further reading
Related calculators
More in Physics · All calculators
This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.