Enter the focal length of the lens into the calculator to determine the diopter of that lens.

Diopter Conversion Formula

The following formula is used to convert focal length into diopter.

D = 1000 / F
  • Where D is the diopter (1/m)
  • F is the focal length (mm)

To calculate the diopter length, divide 1000 by the coal length.

What is a diopter?


A diopter is a unit equal to the reciprocal of the focal length of a lens (in meters), that describes the refractive power of that lens.

How to calculate diopter?

Example Problem:

The following example outlines how to calculate the diopter of a lens.

First, determine the focal length of the lends. In this example, the focal length is measured to be .2cm.

Next, convert the focal length into millimeters. Multiply the result above by 100 to get mm.

.2cm * 100 = 20 mm.

Finally, calculate the diopter using the formula above:

D = 1000 / F

D = 1000 / 20

D = 50 m^-1