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Decibel Distance Calculator

Enter the reference level and distances to find the SPL at the target distance.

How to use

  1. Enter your values in the fields above.
  2. Press Calculate to see your result instantly.
  3. Use the Share button to copy a link to your result.

About this calculator

Sound intensity falls off with distance according to the inverse-square law — doubling the distance from a point source quarters the sound intensity, which works out to a drop of 6 dB per doubling of distance in free field conditions. The formula is SPL2 = SPL1 − 20·log10(d2/d1), where SPL1 is the known sound pressure level at reference distance d1.

This calculator applies that formula to find the SPL at any new distance, which is standard practice in audio engineering, noise assessment, and live sound design — for example, checking whether a PA system will still be within safe or code-compliant noise limits at the edge of a venue, or estimating how much quieter a machine will sound from twice as far away.

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