Enter the thickness of the lens and the radius of curvature into the calculator to determine the lens index. This calculator can also evaluate any of the variables given the others are known.

## Lens Index Formula

The following formula is used to calculate the lens index.

LI = d / r

Variables:

- LI is the lens index
- d is the thickness of the lens (mm)
- r is the radius of curvature of the lens (mm)

To calculate the lens index, divide the thickness of the lens by the radius of curvature of the lens. The result is the lens index, which is a measure of the lens’s refractive power.

## What is a Lens Index?

A lens index refers to the refractive power of a lens, which is its ability to bend light. It is a number that describes how thick or thin the lens is in relation to its degree of vision correction. A higher index means a thinner, lighter lens, which is beneficial for those with stronger prescriptions. Common lens indices range from 1.50, for standard plastic lenses, to 1.74, for the thinnest and lightest lenses available.

## How to Calculate Lens Index?

The following steps outline how to calculate the Lens Index.

- First, determine the thickness of the lens (d) in millimeters.
- Next, determine the radius of curvature of the lens (r) in millimeters.
- Next, gather the formula from above = LI = d / r.
- Finally, calculate the Lens Index.
- After inserting the values of d and r into the formula and calculating the result, check your answer with the calculator above.

**Example Problem : **

Use the following variables as an example problem to test your knowledge.

thickness of the lens (d) = 4 mm

radius of curvature of the lens (r) = 10 mm