🔍 Diopter Calculator
Convert a lens’s focal length to its optical power in diopters, or combine two lenses in contact.
cm
D
What Is a Diopter?
A diopter (D) is the unit of optical power of a lens, used commonly in eyewear prescriptions and optics. It describes how strongly a lens converges or diverges light.
The Formula
Power (D) = 1 / focal length (in meters). A shorter focal length means a stronger, higher-diopter lens. Positive values indicate converging (convex) lenses; negative values indicate diverging (concave) lenses. When two thin lenses are placed in contact, their powers add directly.
This tool is for general educational and planning purposes and is not a substitute for a professional eye examination or prescription.
Last reviewed August 2026