Focal Length Calculator
Calculate the focal length of a thin lens from the object distance and image distance using the lens equation 1/f = 1/dₒ + 1/dᵢ.
- Magnification |m|
- 2.000×
Formula: 1/f = 1/dₒ + 1/dᵢ
About Focal Length Calculator
Focal Length Calculator is a free online calculator that gives you an instant, accurate result as you type. Calculate the focal length of a thin lens from the object distance and image distance using the lens equation 1/f = 1/dₒ + 1/dᵢ.
The calculation uses the standard formula 1/f = 1/dₒ + 1/dᵢ and updates live with every change to the inputs. Everything runs client-side in your browser — fast, private, and free to use as often as you like.
The thin-lens equation applies to both camera lenses and eyeglasses; a converging lens has a positive focal length, a diverging lens a negative one.
Frequently Asked Questions
Is Focal Length Calculator free to use?
Yes. Focal Length Calculator is completely free, with no sign-up, no downloads, and no usage limits. You can use it as many times as you like on any device with a web browser.
How accurate is this calculator?
The calculator applies the standard formula (1/f = 1/dₒ + 1/dᵢ) with full floating-point precision and rounds only the displayed result. For most practical purposes the results are exact.
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