Microscopy & measurement · SL/HL
Scale bar actual size
Use a scale bar to find a specimen’s actual size.
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.
Result & working
ExampleThe calculator is loading. The worked example is also shown below.
Download results
Excel and CSV files can be imported into Google Sheets.
More results
Show calculation steps
Interpretation & assumptions
Copy & export
Formula & example
The relationship
What the variables mean
| Symbol | Meaning |
|---|---|
| image lengths | Any matching ruler unit can be used because their ratio is dimensionless. |
Worked example
- Measured specimen length on image
- 42
- Measured scale-bar length on image
- 12
- Scale-bar stated actual length
- 10
- Scale-bar actual unit
- µm
35 µm
Follow the example steps
- image specimen / image scale bar = 42 / 12 = 3.5
- actual specimen size = 3.5 × 10 µm = 35 µm
Common mistakes
Measure the specimen and scale bar on the same image.
Incorrect approach
30 mm, 10 mm → 20 µm: actual size = 30 µm
Correct approach
actual size = (30/10) × 20 = 60 µm
More checks before you submit
- Measure the scale bar and specimen on the same copy of the image.
Method notes
This method remains valid when an image has been resized, provided the specimen and scale bar were resized together.