Enter the beam diameter at two separate points and the distance between those two points into the calculator to determine the laser divergence.

Laser Divergence Formula

The following equation is used to calculate the beam divergence.

 ϴ = 2*arctan (( Df - Di )/ 2L) 
  • Where  ϴ is the angle of divergence
  • Df is the beam diameter at point f
  • Di is the beam diameter at point i
  • L is the distance between point f and point i

To calculate the laser divergence, take the arc tangent of the difference between the beam diameters at each point over 2 times the distance between point, then multiply by 2.

What is a Laser Divergence?


Laser divergence is the measure of the angle of a laser beam’s spread. A laser beam that has low divergence could be said to be “collimated”, which means it will maintain a narrow beam as opposed to spreading out.

If you’re using an optical instrument, such as an optical collimator, that requires a collimated beam of light, you have to make sure that the laser beam has low divergence.

How to Calculate Laser Divergence?

To calculate the divergence of a laser, subtract the diameter at point f from the diameter of the beam at point i, then, divide by 2 times the distance between the 2 points.

Next, take the arc tangent of that value and then multiply by 2 to get the laser divergence.