Enter the radius of curvature (mm) into the Focal Distance Calculator. The calculator will evaluate and display the Focal Distance.

## Focal Distance Formula

The following formula is used to calculate the Focal Distance.

FD =  R / 2

• Where FD is the Focus Distance (mm)
• R is the radius of curvature (mm)

## How to Calculate Focal Distance?

The following example problems outline how to calculate Focal Distance.

Example Problem #1:

1. First, determine the radius of curvature (mm).
• The radius of curvature (mm) is given as: 55.
2. Finally, calculate the Focal Distance using the equation above:

FD =  R / 2

The values given above are inserted into the equation below and the solution is calculated:

FD = 55 / 2 = 27.5 (mm)

Example Problem #2:

For this problem, the variables needed are provided below:

radius of curvature (mm) = 89

${V2} =${number 4}

This example problem is a test of your knowledge on the subject. Use the calculator above to check your answer.

FD =  R / 2 = ?