Inverse Square Law Calculator

About this calculator

This calculator applies the inverse-square law, I₂ = I₁·(d₁/d₂)², which describes how the intensity of light, sound, radiation, or gravity spreads out and weakens as the same total energy is distributed over the surface of an ever-larger sphere as distance increases — doubling the distance quarters the intensity, tripling it cuts intensity to one-ninth.

Photographers and lighting technicians positioning a flash or studio light, audio engineers setting speaker placement, radiation safety officers calculating dose at a distance from a source, and physics students verifying the law experimentally all use this. Enter a known intensity at one distance and a new distance to find the intensity there.