Sound Level Distance Calculator
See how loud a source is once you step back — the inverse-square drop in sound pressure level as distance grows.
The 6 dB rule
For a point source in the open, every doubling of distance drops the level by about 6 dB. Quadruple the distance and you lose about 12 dB.
What is a sound level distance calculator?
One level and two distances in, the new level out
A sound level distance calculator tells you how loud a sound source is once you move toward or away from it. Sound from a small ("point") source spreads out over an ever-larger sphere, so its energy thins out with distance — the inverse-square law. Expressed in decibels, that thinning becomes a simple subtraction: the level falls by 20·log10 of the distance ratio. This is the everyday tool for estimating how far a loudspeaker, a machine, a generator, or a concert stack will carry, and how much quieter it becomes once you step back.
Enter the reference level, the reference distance, and the target distance to get the level at the new distance instantly.
One formula, built from the reference level L1 and the ratio of the two distances.
L2 = L1 − 20 × log10(d2 / d1)The term 20·log10(d2/d1) is the drop in decibels. Because log10(2) ≈ 0.301, doubling the distance subtracts about 20 × 0.301 ≈ 6 dB. The change in level (ΔL) is simply L2 − L1, which is negative when you move away and positive when you move closer.
Suppose a speaker measures 100 dB at 1 m, and you want the level at 10 m.
Distance ratio
d2 / d1 = 10 / 1 = 10 — you are ten times further away.
Decibel drop
20 × log10(10) = 20 × 1 = 20 dB lost over that ten-fold distance.
New level
L2 = 100 − 20 = 80 dB, a change of −20 dB from the reference.
The new level tells you how the source will sound at a chosen spot. In the example, 100 dB at 1 m becomes 80 dB at 10 m — a 20 dB drop, which the ear perceives as roughly one-quarter as loud (about a 10 dB drop sounds "half as loud"). The single most useful insight is the 6 dB rule: every doubling of distance removes about 6 dB, so the first few metres away from a source buy you far more relief than the last few. That is why stepping back from 1 m to 2 m is dramatic, while moving from 50 m to 51 m barely registers. Use the result to place equipment, judge whether a noise source clears a limit at the property line, or estimate how far speech or an alarm will stay intelligible. Remember it is the level for a single point source radiating freely; close to the source or indoors, the real drop is smaller.
The inverse-square law is exact for an ideal source, but real spaces complicate it.
Free-field point sources only
The 20·log10 rule assumes a single point source radiating into open space with no reflections — outdoors, away from walls. Indoors, reverberation keeps the level up so the drop is much smaller. A line source (a busy road, a long pipe) falls only about 3 dB per doubling, not 6. The model also ignores air absorption (which adds extra loss at high frequencies over long distances), ground effects, wind, and obstacles. Treat the result as a clean free-field estimate and expect real environments to differ.