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Sound Decibel & Distance Attenuation Calculator

Inverse-square level at a second distance: dB2 = dB1 - 20 log10(d2/d1).

Page updated 2026-09-04.

Sound Decibel & Distance Attenuation Calculator visual
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Default 90.

Default 1.

Default 4.

Calculated Results

Level at d2 (dB)

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Change (dB)

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d2 / d1

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Why sound drops by 12 dB, not 4x less loud, at 4x the distance

A sound measuring 90 dB at 1 meter drops to 77.96 dB at 4 meters -- a change of -12.04 dB for a distance ratio of exactly 4x. This isn't a linear drop-off; it follows the inverse square law that governs how sound energy spreads from a point source.

The formula is 20 x log10(d2/d1): 20 x log10(4) = 20 x 0.602 = 12.04 dB of loss. Because decibels are already a logarithmic scale, every doubling of distance from a point source produces the same fixed drop of about 6 dB, regardless of the starting distance -- doubling from 1m to 2m loses about 6 dB, and doubling again from 2m to 4m loses another 6 dB, for the combined ~12 dB shown here.

This consistent 'about 6 dB per doubling of distance' rule of thumb is genuinely useful for quick mental estimates in real-world noise assessment, without needing to run the full logarithmic formula every time.

Why real rooms and outdoor spaces don't follow this exactly

Point-source inverse square in free field. Rooms and wind are omitted. This models a single point source radiating sound uniformly in a free field -- open space with no reflecting surfaces, no absorption, and no obstacles. Real indoor spaces have walls, ceilings, and furniture that reflect sound back, which actually slows the drop-off compared to this idealized free-field prediction.

Outdoor factors this doesn't model include wind (which can carry sound further downwind while suppressing it upwind), temperature gradients (which bend sound waves), and ground absorption -- all of which can meaningfully shift real measured sound levels away from the clean inverse-square prediction.

This also assumes a true point source -- a large or spread-out sound source (like a long wall of speakers, or highway traffic noise) doesn't follow the same inverse-square drop-off as a genuine point source, especially at distances comparable to or smaller than the source's own physical size.

Related acoustics and unit-conversion tools

For a related energy or physics quantity conversion outside the acoustic-specific decibel scale, the Energy Unit Converter covers general energy units.

For pressure-related unit conversions (sound pressure level and the decibel scale both relate conceptually to pressure), the Pressure Unit Converter is a related reference tool.

Frequently Asked Questions (FAQ)

How is the -12.04 dB change calculated?

Change in dB = 20 x log10(d2/d1) = 20 x log10(4/1) = 20 x log10(4) = 20 x 0.602 = 12.04 dB of loss, following the inverse square law for point-source sound propagation.

Why does every doubling of distance lose roughly the same 6 dB?

Because decibels are a logarithmic scale, and log10(2) is a constant value (about 0.301) regardless of the starting distance -- 20 x 0.301 = 6.02 dB. This constant per-doubling loss is a useful mental shortcut for quick real-world estimates.

Does this model apply accurately inside a room?

Point-source inverse square in free field. Rooms and wind are omitted. Not precisely. This assumes a free field with no reflecting surfaces. Real rooms reflect sound off walls, ceilings, and furniture, which actually slows the sound-level drop-off compared to this idealized outdoor, obstruction-free prediction.

Does wind or temperature affect real-world sound propagation in ways this doesn't capture?

Yes. Point-source inverse square in free field. Rooms and wind are omitted. Wind can carry sound further downwind while suppressing it upwind, and temperature gradients can bend sound waves -- neither factor is included in this idealized point-source, free-field calculation.

Does this work for a large sound source, like a long wall of speakers?

Less accurately. This models a true point source. A large or spread-out source doesn't follow the same clean inverse-square drop-off, especially at distances comparable to or smaller than the physical size of the source itself.

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