Mirror Equation Calculator
🔍 Light & optics. Use the Mirror equation formula to find focal length, object distance, image distance: pick the value you want, type the others, and the answer updates as you go.
Real-is-positive: a concave mirror has a positive f.
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 |
|---|---|
| Focal length | cm |
| Object distance | cm |
| Image distance | cm |
Worked example
Find the focal length when Object distance = 30 cm, Image distance = 15 cm.
Using 1/f = 1/u + 1/v: Focal length = 10 cm.
Frequently asked questions
What is the formula for Mirror equation?
1/f = 1/u + 1/v. Real-is-positive: a concave mirror has a positive f.
What do the letters stand for, and what units are used?
Focal length in cm, Object distance in cm, Image distance in cm.
How do you calculate focal length?
Put the values into 1/f = 1/u + 1/v. For example, with Object distance = 30 cm, Image distance = 15 cm, focal length = 10 cm.
Can I solve for a different value?
Yes. In the calculator above, pick the circle next to any value (focal length, object distance, image distance) and fill in the others: it rearranges the formula for you.
