Decibel Distance Calculator
Estimate free-field sound level at a new distance from a point source.
Apply inverse-distance spreading in decibels
Sound pressure from an ideal point source falls inversely with distance in an unobstructed free field. This calculator converts that ratio into decibels using the reference level minus 20 times the base-ten logarithm of target distance divided by reference distance. It is useful for quick acoustic planning when a measured level and distance are known but a second location has not been measured.
A level of 90 decibels measured one meter from the source becomes 70 decibels at 10 meters in the ideal model, a 20 decibel reduction for a tenfold distance increase. Doubling distance produces about a 6.0206 decibel drop. Moving closer reverses the sign and raises the predicted level by the same geometric relationship.
Recognize when free-field assumptions fail
Walls, ground reflections, rooms, barriers, wind, atmospheric absorption, line arrays, and extended sources can all depart substantially from point-source free-field spreading. Decibels also require a stated weighting and reference when used as measured sound levels. The ratio calculation runs in your browser. Use field measurements or a validated propagation model for exposure, compliance, and venue decisions.
Frequently Asked Questions
Why does doubling distance reduce about 6 dB?
Sound pressure halves for an ideal point source, and 20 times log base ten of two is about 6.0206.
Does this include air absorption?
No. It models geometric spreading only and omits frequency-dependent atmospheric losses.
Will this work inside a room?
Room reflections can dominate the level, so free-field distance loss may not describe an enclosed space accurately.
Browse the full set of free, private, in-browser tools.