Decibel Calculator
Calculate the sound level (dB) at a different distance from a sound source.
How to use the decibel calculator
- Enter the sound level in decibels (dB) at a known distance from the sound source.
- Enter that known distance in meters.
- Enter the distance you want to find the sound level at.
- The new sound level updates automatically.
Why does sound decrease with distance?
Sound spreads outward like a sphere from its source, and the energy is distributed over an ever-larger area the farther away you get. This is called the inverse square law, and causes sound pressure to decrease with distance — every doubling of distance reduces the sound level by about 6 dB. The formula is dB₂ = dB₁ − 20 × log₁₀(d₂ / d₁).
Why +3 dB means a doubling
The decibel is a logarithmic scale, which means addition on the scale corresponds to multiplication in reality. An increase of 3 dB corresponds to a doubling of sound power, and 10 dB corresponds to ten times the power. That is why two identical loudspeakers together do not give twice as many decibels, but only 3 dB more than one of them.
Perceived loudness follows a different curve from physical power. The rule of thumb is that around 10 dB — ten times the power — is needed before most people perceive a sound as «twice as loud». It is also why small decibel figures matter more than they appear to in noise contexts: a 3 dB reduction halves the actual sound power, even though the number looks modest.
Frequently asked questions
Why is the decibel scale logarithmic?
Because the human ear perceives loudness logarithmically, not linearly — a sound that's twice as "powerful" in physical energy isn't perceived as twice as loud. The decibel scale (based on logarithms) therefore matches how we actually experience sound.
How much does sound decrease when I double the distance?
About 6 dB for every doubling of distance, in a free sound field without reflections. This follows directly from the inverse square law: 20 × log₁₀(2) ≈ 6.
Does the formula apply to all types of sound?
The formula applies to a point source in a free sound field (e.g. outdoors, far from reflective surfaces). Indoors or near walls, reverberation and reflections will cause the sound to decrease less than calculated.