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

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## 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:

- First, determine the radius of curvature (mm).
- The radius of curvature (mm) is given as: 55.

- 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** = ?**