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Lens Equation Calculator
Solve the thin lens equation for focal length, object distance or image distance, with magnification.
Thin lens calculator
Result: —
Magnification: —
Image: —
How to use the Lens Equation Calculator
- Choose the quantity you want the lens equation to solve for.
- Enter the other two distances in the same unit, such as centimetres.
- Read the result together with the magnification and image type.
Features
- Solves focal length, object distance or image distance
- Shows magnification for the solved setup
- Reports whether the image is real or virtual
- Accepts negative focal lengths for diverging lenses
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Frequently Asked Questions
Common questions about the free online lens equation calculator.
The thin lens equation is 1/f = 1/do + 1/di, where f is the focal length and do and di are
the object and image distances.
It means the image is virtual and forms on the same side of the lens as the object, so it
cannot be projected onto a screen.
Choose Focal length f, then enter the object distance and the image distance. The tool solves
the lens equation for you.
Magnification is the image distance divided by the object distance. A value above one means
the image is larger than the object.
The image is upright when the magnification is positive, which happens for virtual images
formed by a diverging lens or a close object.
Yes. A negative focal length describes a diverging lens, and the calculator reports a
virtual, upright and smaller image.
Any single unit of length works, such as centimetres or millimetres, as long as you use the
same unit for every distance.
Yes. It runs entirely in your browser with no network connection, no uploads and no tracking
of any kind.
Yes. The lens equation calculator is completely free, unlimited and needs no account or
sign-up.
Last updated: October 10, 2026