Sound Distance Calculator
Estimate geometric spreading from a stated sound level and reference distance
Sound gets quieter as you move away from its source — but by how much? For a compact point source in an ideal free field, geometric spreading follows the inverse square law: every time you double the distance, the sound pressure level drops by approximately 6 dB. For a hypothetical source of 100 dB at 1 metre, this model gives 80.0 dB at 10 metres and 60.0 dB at 100 metres.
Use this calculator to estimate noise levels at any distance. It illustrates point-source spreading for a stated reference level and distance, not actual traffic levels or a guaranteed safe distance. For a full reference of common sound levels, see the decibel level chart.
Distance Noise Calculator
Calculate
Source geometry
Compact source, sufficiently far from the source for free-field spreading. Near-field effects and directional speaker arrays are not modeled. Both models exclude reflections, ground effects, barriers, atmospheric absorption and weather. The source and its operating conditions must remain the same.
Hypothetical example presets — not measured source levels:
Calculated level at 10 m
80.00 dB
Reference: 100 dB at 1 m · Ideal point source
Reduction relative to reference: 20.00 dB
L₂ = L₁ − 20 × log₁₀(d₂ / d₁)
Not a measurement, audibility prediction or safe-exposure assessment. Rounded model output, not measurement precision. Input and output retain the same sound-pressure metric and time basis; do not enter sound power, SEL or EPNL.
How 100 dB Changes With Distance
Reference: 100 dB at 1 m. Each listed distance is absolute; the model assumes an ideal point source.
| Distance | Level | Change from reference |
|---|---|---|
| 1 m | 100.00 dB | −0.00 dB |
| 2 m | 93.98 dB | −6.02 dB |
| 4 m | 87.96 dB | −12.04 dB |
| 8 m | 81.94 dB | −18.06 dB |
| 16 m | 75.92 dB | −24.08 dB |
| 32 m | 69.90 dB | −30.10 dB |
| 64 m | 63.88 dB | −36.12 dB |
How Sound Propagation Works
In open air with no obstacles, sound radiates outward from a point source in all directions. As it spreads, the same energy covers a larger area, and the sound pressure level decreases. This relationship is described by the inverse square law:
L₂ = L₁ − 20 × log₁₀(d₂ / d₁)
Where L₁ is the reference sound-pressure level, d₁ is the reference distance, and d₂ is the listener distance
For this ideal point-source model, sound drops by 6 dB every time the distance doubles. In practice, this is an idealized model — indoors, reflections from walls, ceilings, and floors can keep levels higher, without a universal per-doubling rule. Outdoors, wind, temperature gradients, ground absorption, and barriers like buildings also affect the result.
For ideal long line sources, which can approximate some traffic conditions, the geometry is different: sound drops by approximately 3 dB per doubling of distance instead of 6 dB, because the source extends along a line rather than emanating from a single point. Its equation is L₂ = L₁ − 10 × log₁₀(d₂ / d₁). Finite lines eventually behave differently; this simplified option is not a substitute for a road-noise model.
Model reference: FHWA Noise Barrier Design Handbook, §3: spherical and cylindrical divergence. The inverse formulas are algebraic rearrangements of those spreading equations.
Practical Examples
Construction site
For a hypothetical compact source at 100 dB at 1 m, the ideal model gives 86.0 dB at 5 m and 70.5 dB at 30 m. These are calculated examples, not jackhammer measurements.
Construction noise guideConcert speakers
For a hypothetical point-source speaker at 110 dB at 1 m, the model gives 90.0 dB at 10 m. Speaker arrays, reflections and actual exposure require separate assessment.
Concert noise levelsHighway traffic
A long road can behave more like a line source than a point source. This point-source calculator cannot supply a defensible traffic level without a suitable source model, reference measurement and site conditions.
Traffic noise guideDog barking
A hypothetical brief point-source sound at 85 dB at 1 m gives 65.0 dB at 10 m. This is not a typical bark measurement and says nothing conclusive about audibility or hearing risk.
Dog bark noise levelsWhen Should You Be Concerned?
This calculator cannot establish a safe distance or an allowable listening time. Hearing-risk assessment requires actual personal sound exposure, weighting, duration, repeated events and suitable instrumentation. NIOSH and OSHA occupational criteria are reference frameworks, not guarantees of safety from an ideal propagation estimate.
Keep in mind that this calculator models ideal free-field conditions. Real-world results depend on your environment — use the noise meter tool to view local signal levels or a locally calibrated estimate, not a certified exposure measurement. For reference guidance, see the decibel level chart.
Frequently Asked Questions
How does sound decrease with distance?
For a compact point source in an ideal free field, geometric spreading gives approximately 6 dB reduction per doubling of distance. This is geometric spreading only; reflections, barriers, weather and background sound are not included.
Does the 6 dB rule always apply?
The 6 dB per doubling rule applies to point sources in free-field conditions (outdoors, no reflections). Indoor reflections have no universal per-doubling reduction. An ideal long line source has approximately 3 dB geometric spreading per doubling, but a real road also needs traffic, ground, geometry and weather data. The ideal line option is not a traffic prediction.
How far away can you hear 100 dB?
For a hypothetical 100 dB point source measured at 1 metre, the model gives 60.0 dB at 100 metres. It cannot predict how far it is audible: background sound, frequency, hearing, terrain and weather also matter.
How far does 120 dB travel?
A hypothetical point source at 120 dB at 1 metre gives 80.0 dB at 100 metres. This is geometric spreading, not a maximum travel distance. A target-level calculation finds where an ideal model reaches your chosen level, not where sound stops or becomes inaudible.
Is this calculator accurate for indoor use?
This calculator models free-field (outdoor) propagation. Indoor environments have reflections that keep sound levels higher. Use a suitable sound level meter when actual sound pressure or exposure must be established; a browser estimate does not validate the model.
Want to Check Sound at Your Position?
View local signal levels with Snap Decibel Meter. Optional local calibration provides an estimate, not a certified exposure assessment.
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