Inverse Square Law Calculator
Calculate how the intensity of light, radiation, or sound changes as distance from the source changes, using the inverse square law.
What the inverse square law says
The inverse square law describes how the intensity of a point source’s radiation (light, sound, gravity, radiation) decreases with the square of the distance from the source. Double the distance, and intensity drops to a quarter.
The formula
I2 = I1 × (d1/d2)², where I1 is the known intensity at distance d1, and I2 is the intensity at the new distance d2. This relationship holds for any quantity that spreads out spherically and uniformly from a point source in free space.
This is the standard physics inverse square relationship, applicable to light, radio signals, radiation, and sound intensity (though sound pressure level uses a related but distinct decibel formula).