Magnification tells us how many times bigger an image is than the real object. It has no unit: write ×100, for example.
| Convert | How |
|---|---|
| cm → mm | ×10 |
| mm → μm | ×1000 |
| μm → nm | ×1000 |
Go the other way by dividing by the same number. μm means micrometre; nm means nanometre.
Example: an image is 40 mm long. The real cell is 0.1 mm long. The units already match.
Magnification = ×400.
On a microscope: total magnification = eyepiece × objective. A ×10 eyepiece and ×40 objective give ×400.
An image is 30 mm long at ×600.
Real size = 0.05 mm = 50 μm.
To find image size instead: image size = real size × magnification.
A scale bar shows a known real distance. Compare the cell with the bar: this cell is twice as long as a 10 μm bar, so its real length is 20 μm.
The bar stays useful when the picture is resized along with it. Measuring the picture on different phones would give different image lengths.
These example cells have lengths of 2 μm and 20 μm. The second is 10 times larger in length: one order of magnitude.
Standard form writes a number between 1 and 10 multiplied by a power of ten:
2000 = 2 × 10³
0.000002 m = 2 × 10⁻⁶ m = 2 μm
Match units first. Magnification = image size / real size. Use the scale bar when an image is resized.
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