Lens Magnification Calculator
Calculate the lateral magnification produced by a thin lens using m = −di/do. A negative result indicates an inverted image; magnitude greater than 1 means the image is enlarged.
How to use this tool
- Enter image distance (di) and object distance (do) in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your magnification and the full breakdown beneath it.
Formula
m = −di / do
How it works
Divide the negative of the image distance by the object distance. A negative value means an inverted image.
Worked example
Common mistakes to avoid
- Forgetting the negative sign in m = -di/do — dropping it makes an inverted image appear upright in the calculation.
- Confusing lateral magnification (size ratio) with angular magnification used for eyepieces and microscopes — this calculator computes lateral magnification only.
- Using the object-to-image distance (total track length) instead of the individual do and di values measured from the lens.
Key terms
Frequently asked questions
- What does a magnification of -2 mean?
- The image is twice the size of the object (|m| = 2) and is inverted (negative sign). This is typical for a camera or projector lens when the object is beyond twice the focal length.
- Can magnification be a fraction less than 1?
- Yes. A magnification of -0.5 means the image is half the height of the object and is inverted. This occurs when the object is far from the lens, as in a camera photographing a distant scene.
- What magnification does a magnifying glass produce?
- A magnifying glass used near the eye produces a virtual, upright image with positive magnification greater than 1. For a simple lens with focal length f, the angular magnification is approximately 250 mm / f when used at the near point.