Magnification Calculator (Microscopy)
By Santaji GadepatilinUpdated October 27, 2026
calculated
Type in any field to change it. Press × on a value to calculate that field instead.
How to use this calculator
Enter any two of image size, actual size and magnification. Choose units for each size (mm, µm, nm and more).
Formula
Magnification = image size ÷ actual size
Example
A cell 100 µm across appears 40 mm wide in a photo:
M = 40,000 µm ÷ 100 µm = 400×
Remember the units
1 mm = 1,000 µm · 1 µm = 1,000 nm
Frequently asked questions
What is the magnification formula?
Magnification = image size ÷ actual size. Both sizes must be in the same unit — the calculator converts mm, µm and nm for you.
How do I find actual size?
Divide the image size by the magnification. Press × on Actual size and type the magnification.
How do I calculate total microscope magnification?
Multiply eyepiece and objective magnifications — a 10× eyepiece with a 40× objective gives 400×.