Calculate Intensity Drop at Divergence

Calculator for the strength of spherical expanding signals, like light, radio and sound, at certain distances, with the inverse-square law. The signal expands as a spherical shell, the intensity decreases to the square of the distance. At twice the distance, the signal has one fourth of the strength. This is in theory, if the signal doesn't get reflected. Please enter both values of measuring point A and one value of measuring point B, the other value will be calculated.

Measuring point A distance: strength:
Measuring point B distance: strength:

Round to    decimal places.

The formula for the inverse-square law is: I1 / I2 = r2² / r1²
I is the intensity (strength), r is the radius Radius (distance).


The declining signal strength at a spherical expansion. Theoretically, the signal range is infinite, at least for electromagnetic waves like light. Sound, in contrast, needs a medium like air to spread out. But even the strongest signal won't be measurable at a long enough distance.

Example: for a signal to reduce its intensity to a tenth, it takes 3.162 times the distance (square root of 10).

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