See how loud a source is at any distance. Enter a measured SPL and distance to estimate the level somewhere closer or further away.
SPL Distance Calculator (Inverse-Square Law)
In a free field, SPL drops 6 dB per doubling of distance: dB₂ = dB₁ − 20 × log₁₀(d₂ ÷ d₁). Real rooms add reflections, so treat this as the direct-sound estimate. Use the same unit for both distances.
How it works
In a free field, sound pressure level drops 6 dB every time the distance doubles: dB₂ = dB₁ − 20 × log₁₀(d₂ ÷ d₁). Real rooms add reflections that raise the far-field level, so treat the result as the direct-sound estimate.
FAQ
Why 6 dB per doubling?
Sound energy spreads over a sphere whose area grows with the square of distance, so intensity — and SPL — falls predictably as you move away.
Does this work indoors?
Roughly, for the direct sound near the source. Beyond the critical distance, room reflections dominate and levels fall off more slowly.