Lens Formula Calculator
🔍 Light & optics. Use the Lens formula formula to find image distance v, focal length f, object distance u: pick the value you want, type the others, and the answer updates as you go.
“Real is positive”: a positive v is a real image; a negative f is a diverging lens.
Pick the ○ next to the value you want to find, fill in the others, and it solves as you type.
What each letter means
| Quantity | Unit |
|---|---|
| Image distance v | cm |
| Focal length f | cm |
| Object distance u | cm |
Worked example
Find the image distance v when Focal length f = 10 cm, Object distance u = 25 cm.
Using 1/f = 1/u + 1/v: Image distance v = 16.667 cm.
Frequently asked questions
What is the formula for Lens formula?
1/f = 1/u + 1/v. “Real is positive”: a positive v is a real image; a negative f is a diverging lens.
What do the letters stand for, and what units are used?
Image distance v in cm, Focal length f in cm, Object distance u in cm.
How do you calculate image distance v?
Put the values into 1/f = 1/u + 1/v. For example, with Focal length f = 10 cm, Object distance u = 25 cm, image distance v = 16.667 cm.
Can I solve for a different value?
Yes. In the calculator above, pick the circle next to any value (image distance v, focal length f, object distance u) and fill in the others: it rearranges the formula for you.
