Microscopy & measurement · SL/HL
Magnification & Actual Size Calculator
Choose the unknown quantity. Image and actual sizes can be entered in different metric units.
Your values
Start with the example or enter your own values. Use a dot for decimals and e for scientific notation.
Calculated locally. No account or input upload.
Result & working
ExampleThe calculator is loading. The worked example is also shown below.
Step-by-step working
The formula
magnification = image size / actual size
actual size = image size / magnification
| 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. |
When to use this calculator
The image and actual dimensions must represent the same feature. Convert units before taking the ratio.
Worked example
The page opens with these example values. The result below is pre-generated for reference.
- Image size = 18 mm = 0.018 m
- actual size = image/M = 0.018 / 600 = 0.00003 m
- = 30 µm
30 µm
Common mistakes
- 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.