Magnification tells you how much larger (or smaller) an image is than the object. A magnifying glass makes small things look bigger by letting you bring them closer than your eye could otherwise focus.
How to use the Lens Magnification Calculator
- Mode
- Object distance d_o
- Image distance d_i
- Object height (optional)
- Focal length of the magnifier
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
Choose the mode. For a lens image, enter both distances (negative image distance for a virtual image). For a magnifier, enter the focal length.
Inputs explained
| Field | What to enter |
|---|---|
| Mode | Choose one: Image and object distances, Magnifying glass (angular magnification) |
| Object distance d_o | Units: cm, mm, m, in, ft |
| Image distance d_i | Units: cm, mm, m, in, ft |
| Object height (optional) | Units: cm, mm, m, in, ft |
| Focal length of the magnifier | Units: cm, mm, m, in, ft |
What each result means
- Image height = [Magnification]×[Object height (optional)]
- Magnification at the near point = 1 + 0.25÷[Focal length of the magnifier]
- Lens power = 1÷[Focal length of the magnifier]
Example values
How the main result changes when Object distance d_o changes and everything else stays at the example values above:
| Object distance d_o (cm) | Magnification (×) |
|---|---|
| 15 | -1 |
| 22.5 | -0.6667 |
| 30 | -0.5 |
| 37.5 | -0.4 |
| 45 | -0.3333 |
| 60 | -0.25 |
Formula
M = −d_i/d_o = h_i/h_o · Magnifier: M = 25 cm/f (relaxed eye) or 1 + 25 cm/f (near point)
Worked example
Inputs: Mode: Image and object distances; Object distance d_o: 30 cm; Image distance d_i: 15 cm; Object height (optional): 2 cm.
Results: Magnification = -0.5 ×; Image height = -1 cm.
Key terms
- Magnification
- Ratio of image size to object size.
Frequently asked questions
What does a negative magnification mean?
The image is inverted.
How strong is a 10× loupe?
Its focal length is about 2.5 cm.
Why 25 cm?
It is the standard near point, the closest comfortable reading distance.
Is magnification the same as zoom?
Zoom changes focal length; magnification is the resulting size ratio.