Thin Lens Equation Calculator
Image distance and magnification for a lens or mirror.
Enter your values
Enter the focal length in cm.
Enter the object distance in cm.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Image distance
- 15 cm
- Magnification
- -0.5
- Image type
- Real, inverted
Quick answer
1/f = 1/do + 1/di, magnification = -di/do.
1/f = 1/do + 1/di
At a glance
| What it does | Image distance and magnification for a lens or mirror. |
|---|---|
| Category | Physics |
| Inputs needed | Focal length, Object distance |
| Main output | Image distance |
| Formula | 1/f = 1/do + 1/di |
| Cost | Free — no sign-up, no download |
How to use the Thin Lens Equation Calculator
- 1Enter the focal length (positive for converging, negative for diverging lenses).
- 2Enter the object distance from the lens.
- 3Read the image distance and magnification.
Inputs explained
- Focal length(cm)
- Enter the focal length in cm.
- Object distance(cm)
- Enter the object distance in cm.
Worked example
Using the values the calculator loads with:
Inputs
- Focal length10 cm
- Object distance30 cm
Results
- Image distance15 cm
- Magnification-0.5
- Image typeReal, inverted
Frequently asked questions
What does negative magnification mean?
The image is inverted relative to the object, common for real images from converging lenses.
Does this work for mirrors too?
Yes, the same equation applies to spherical mirrors using the same sign convention.
What do I need to enter into the Thin Lens Equation Calculator?
Just 2 values: focal length, object distance. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Thin Lens Equation Calculator work out the answer?
1/f = 1/do + 1/di, magnification = -di/do. It applies the formula 1/f = 1/do + 1/di and shows the working so you can check each step by hand.
Is the Thin Lens Equation Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.