Free Focal Length Calculator
Calculate the focal length of a thin lens from image and object distances: 1/f = 1/do + 1/di.
cm
cm
Focal Length
10.00 cm
Lens Power10.00 diopters
Focal Length vs Object Distance
Focal Length
The focal length defines the converging or diverging power of a lens or mirror.
Formula
1/f = 1/d_o + 1/d_i
Lens power in diopters is D = 1/f (with f in meters). Positive focal length = converging lens; negative = diverging.
Example Calculation
An object at 30 cm produces an image at 15 cm.
- 011/f = 1/do + 1/di
- 021/f = 1/30 + 1/15
- 031/f = 0.0333 + 0.0667 = 0.1
- 04f = 10 cm
- 05Power = 100/10 = 10 diopters
Frequently Asked Questions
Learn More
Understanding Newton's Laws of Motion
A comprehensive guide to Newton's three laws of motion. Learn about inertia, force and acceleration, action-reaction pairs, and how these principles govern everyday physics.