Microscope Field of View Calculator

How to use this calculator

Enter the eyepiece’s field number and the objective magnification. The field of view diameter is calculated, plus the total magnification.

Formula

FOV = field number ÷ objective magnification

Example

Field number 20 mm with a 40× objective: FOV = 20 ÷ 40 = 0.5 mm = 500 µm.

Typical fields of view (FN 20)

Objective	FOV
4×	5 mm
10×	2 mm
40×	0.5 mm
100×	0.2 mm

Frequently asked questions

What is the field number?

The diameter of the eyepiece's field stop in mm, usually printed on the eyepiece (for example "10×/20").

Why does field of view shrink with higher magnification?

The objective magnifies a smaller region, so FOV = field number ÷ objective magnification.

How do I estimate cell size from FOV?

If 5 cells fit across a 500 µm field, each is about 100 µm long.

Embed this calculator