The decibel distance calculator computes sound level at any distance using the inverse square law: every doubling of distance reduces sound by 6 dB. Enter source dB level and distance to find level at a new distance. Supports meters and feet.
Decibel Distance Calculator
How to Use the Decibel Distance Calculator
This decibel distance calculator applies the inverse square law to find sound level at any distance from a source, given the level at a reference distance.
Formula
L₂ = L₁ − 20 × log₁₀(d₂/d₁). If you move from 1 m to 10 m, the reduction = 20 × log₁₀(10) = 20 dB. Every time you double the distance, you lose 6 dB (20 × log₁₀(2) = 6.02 dB).
Common Reference Levels
Whisper: 30 dB at 1 m. Normal speech: 60-65 dB at 1 m. Truck: 90 dB at 7 m. Concert: 110 dB at 10 m. This calculator assumes free-field (outdoors, no reflections) conditions.
Noise Ordinance Use
If a generator produces 85 dB at 1 m, at 50 m: 85 − 20 × log₁₀(50) = 85 − 33.98 = 51.02 dB. Most residential ordinances allow 55-60 dB during daytime, so this would be compliant at 50 m.
Frequently Asked Questions
How does sound level change with distance?
Sound follows the inverse square law: every time you double the distance, sound intensity drops by 6 dB. A 90 dB source at 1 m becomes 84 dB at 2 m, 78 dB at 4 m, 72 dB at 8 m. This is because sound spreads over an area proportional to the square of the distance.
What decibel levels are dangerous?
Safe continuous exposure: below 85 dB. 85 dB: 8 hours max (OSHA limit). 91 dB: 2 hours max. 100 dB: 15 minutes max. 110 dB: 2 minutes max. 120 dB (jackhammer): immediate hearing damage risk. 140 dB (jet engine close up): immediate pain and damage.
Is this calculator free?
Yes, completely free with no signup required. All calculations run in your browser.
Is my data private?
Yes. All calculations run locally. Nothing is transmitted.
Does the inverse square law apply in all environments?
The inverse square law applies in free-field conditions (outdoors, away from reflective surfaces). Indoors, reflections from walls, floors, and ceilings create a reverberant field that reduces distance attenuation. Near surfaces or in small rooms, the 6 dB per doubling rule is an approximation.