Lens Equation Calculator
Focal length, image distance and magnification.
Enter your values
Enter the focal length in mm.
Enter the object distance in mm.
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
- 51.72 mm
- Magnification
- 0.0345×
- Image type
- Real and inverted
- Field ratio
- 1:29
Quick answer
The thin lens equation links object distance, image distance and focal length.
1/f = 1/do + 1/di
At a glance
| What it does | Focal length, image distance and magnification. |
|---|---|
| Category | Science |
| 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 Lens Equation Calculator
- 1Enter the lens focal length.
- 2Enter the object distance from the lens.
- 3Read image distance and magnification.
Inputs explained
- Focal length(mm)
- Enter the focal length in mm.
- Object distance(mm)
- Enter the object distance in mm.
Worked example
Using the values the calculator loads with:
Inputs
- Focal length50 mm
- Object distance1500 mm
Results
- Image distance51.72 mm
- Magnification0.0345×
- Image typeReal and inverted
- Field ratio1:29
Frequently asked questions
What is 1:1 macro?
Magnification of 1, when object and image distances both equal 2f.
Why is magnification negative?
The sign convention marks an inverted real image.
What do I need to enter into the 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 Lens Equation Calculator work out the answer?
The thin lens equation links object distance, image distance and focal length. It applies the formula 1/f = 1/do + 1/di and shows the working so you can check each step by hand.
Is the 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.