Enter the lens diameter, bridge width, and temple length into the calculator to determine the glasses frame size. This calculator can also evaluate any of the variables given the others are known.

Glasses Frame Size Formula

The following formula is used to calculate the glasses frame size.

FS = (L + W + B) / 3


  • FS is the glasses frame size (mm) L is the lens diameter (mm) W is the bridge width (mm) B is the temple length (mm)

To calculate the glasses frame size, add the lens diameter, the bridge width, and the temple length. Then divide the sum by 3.

What is a Glasses Frame Size?

A glasses frame size refers to the specific measurements that determine the fit of the eyeglasses on the wearer’s face. It typically includes three main dimensions: lens width (the width of one lens), bridge width (the distance between the two lenses), and temple length (the length of the arm piece). These measurements ensure that the glasses fit comfortably and securely on the wearer’s face, providing optimal vision correction and comfort.

How to Calculate Glasses Frame Size?

The following steps outline how to calculate the Glasses Frame Size.

  1. First, determine the lens diameter (L) in millimeters (mm).
  2. Next, determine the bridge width (W) in millimeters (mm).
  3. Next, determine the temple length (B) in millimeters (mm).
  4. Next, add the lens diameter (L), bridge width (W), and temple length (B) together.
  5. Finally, divide the sum by 3 to calculate the Glasses Frame Size (FS).
  6. After inserting the values for lens diameter (L), bridge width (W), and temple length (B) into the formula, calculate the result for Glasses Frame Size (FS).

Example Problem:

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

lens diameter (L) = 50 mm

bridge width (W) = 20 mm

temple length (B) = 140 mm