Decibel Distance Calculator
Find how sound level drops with distance.
Results update as you type.
How it works
Sound gets quieter as you move away from its source, and this calculator finds how much using the inverse-square law. You enter a reference sound level measured at a reference distance, plus a new distance, and it returns the sound level at the new distance and the change in decibels. For a point source radiating freely, sound intensity falls off with the square of distance, which on the logarithmic decibel scale means the level drops by 20 times the logarithm of the distance ratio. A key consequence is that each doubling of distance reduces the level by about 6 decibels, so a sound that is 100 decibels at 1 meter is about 94 at 2 meters, 88 at 4 meters, and so on. This is useful for estimating noise exposure at a distance, planning where equipment or speakers should go, understanding how far a loud sound carries, and assessing whether noise at a property line meets limits. It applies to an idealized point source in open space; in the real world, reflections, barriers, air absorption, ground effects, and directional sources modify the result, so treat it as an estimate, most accurate outdoors away from reflecting surfaces. For a line source like a highway, sound falls off more slowly, by about 3 decibels per doubling. Enter the reference level and distances to find the sound level at the new distance.
dB2 = dB1 − 20 × log₁₀(distance2 / distance1)
For a point source in free space, sound level decreases with distance by the inverse-square law. The new level is the reference level minus 20 times the base-10 logarithm of the ratio of the new distance to the reference distance. Doubling the distance reduces the level by about 6 decibels.
Source:Acoustics (inverse-square law)
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter reference sound level, reference distance and new distance.
- 2
Adjust the options
Fine-tune any options to match your situation.
- 3
Read your result
Sound level at new distance updates instantly as you type — no button to press.
Frequently asked questions
How does sound level change with distance?
For a point source in open space, sound level follows the inverse-square law: the new level is the reference level minus 20 times the base-10 logarithm of the distance ratio. Each doubling of distance reduces the level by about 6 decibels. The calculator applies this to find the level at any distance from a reference measurement.
Why does doubling distance drop 6 decibels?
Sound intensity from a point source spreads over a sphere whose area grows with the square of the radius, so intensity falls to a quarter when distance doubles. On the decibel scale, a quarter of the intensity is a drop of about 6 decibels. This 6-decibel-per-doubling rule is a handy shortcut for estimating sound falloff.
Does this account for walls, barriers, and echoes?
No. The inverse-square law assumes an idealized point source in free space. Real environments have reflections, sound barriers, air absorption, ground effects, and directional sources that change the actual level. The calculator gives a baseline estimate, most accurate outdoors away from reflecting surfaces; indoors or near barriers the real level will differ.
How does a line source differ from a point source?
A line source, like a steady stream of highway traffic, spreads sound cylindrically rather than spherically, so its level falls off more slowly, by about 3 decibels per doubling of distance instead of 6. This calculator uses the point-source rule; for line sources such as roads, expect a slower decrease with distance than it predicts.
What can I use this for?
It helps estimate noise exposure at a distance from machinery, concerts, or equipment, plan speaker and equipment placement, judge how far a loud sound travels, and assess whether noise at a boundary meets local limits. Because it is an idealized estimate, use it for planning and rough assessment rather than precise regulatory measurement, which requires actual sound-level readings.