SPL Distance Calculator

The 6dB-per-doubling rule

Sound spreads outward over an ever-expanding sphere as it travels from its source, following the same inverse square relationship that governs light intensity - this causes SPL to drop by exactly 6dB every time distance doubles.

Worked example

For 100 dB measured at 1 meter, calculating the level at 2 meters:

SPL2 = 100 - 20 x log10(2/1) = 93.98 dB SPL

Distance Multiple	SPL Change
2x distance	-6 dB
4x distance	-12 dB
10x distance	-20 dB

This is why moving even a modest distance farther from a loud sound source produces a surprisingly large drop in perceived loudness - halving perceived loudness (a 10dB drop) requires roughly tripling the distance.