Decibel Distance Calculator
6 dB quieter every time the distance doubles.
Work out Decibel Distance. 6 dB quieter every time the distance doubles. Answers in the units the job actually uses.
Level at 10 m
80 dB
20 dB quieter than at 1 m
In free field, sound spreads over a sphere, so intensity falls with the square of distance and the level drops 6 dB every time the distance doubles. Ten times the distance costs 20 dB. Indoors that is a best case and often a poor prediction. Reflections from walls, floor and ceiling add energy back, and beyond the critical distance in a reverberant room the level barely falls at all — which is why stepping back from a loud machine in a workshop helps far less than the arithmetic suggests. The safe distance row uses whatever limit you set. It is a distance calculation, not a hearing assessment: real exposure limits trade level against time, and the damage from an eight-hour shift at 85 dB is not the same problem as a few seconds at 110.
How the Decibel Distance Calculator works
Work out how much quieter a sound gets as you move away, and how far you need to be for it to reach a chosen limit. This is the free-field answer — indoors, reflections make the real drop smaller, often much smaller.
Also known as: how far to be safe from loud noise · does sound halve with distance · db drop over 10 metres · inverse square law sound calculator
Frequently asked questions
How much does sound drop over distance?
6 dB per doubling of distance in free field, because intensity falls with the square of distance as the sound spreads over a sphere. Ten times the distance costs 20 dB.
Why does moving away from a noisy machine indoors help so little?
Reflections. Beyond the critical distance in a reverberant room the reflected energy dominates the direct sound and the level barely falls at all, no matter how far back you go. The inverse square law describes free field only.
Is 85 dB a safe level?
It is the usual limit for an eight-hour working day, and the trade is between level and time — every 3 dB above it roughly halves the safe duration. A few seconds at 110 dB is a different problem from a shift at 85, and this calculator answers only the distance question.
Does doubling the number of speakers double the loudness?
No. Two identical sources add about 3 dB, which is barely a noticeable increase — perceived loudness roughly doubles at 10 dB, which needs ten times the sources or ten times the power.
Why does the drop not match my sound level meter?
Ground reflections, barriers, wind, temperature gradients and the directionality of the source all interfere. Over long distances outdoors, air absorption also removes high frequencies faster than the geometry alone predicts.
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