Microscopy & measurement · SL/HL

Magnification & actual size

Convert between image size, actual size and magnification.

Your values

Number formats & units

Use decimal dots in datasets. Single values also accept decimal commas and scientific notation such as 1.2e-3 or 1.2 × 10⁻³.

Calculated locally. No account or input upload.

Example

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M=\frac{\text{image size}}{\text{actual size}}

\text{actual size}=\frac{\text{image size}}M

What the variables mean

Symbol	Meaning
$M$	Dimensionless magnification factor.
image size	Measured size of the image or drawing.
actual size	True biological size in a matching length unit.

30 µm

Follow the example steps

Use matching length units; magnification has no length unit.

10 mm, 20 µm: M = 10/20 = 0.5

10000 µm, 20 µm: M = 10000/20 = 500

More checks before you submit

Do not attach a length unit to magnification.
A printed or resized image can change image size even though the labelled scale bar remains informative.

Method notes

The image and actual dimensions must represent the same feature. Convert units before taking the ratio.