Lensmaker's Equation Calculator

About this calculator

This calculator applies the lensmaker's equation, 1/f = (n−1)(1/R₁−1/R₂), which comes from the thin-lens approximation of Snell's law at each curved surface. The refractive index n describes how strongly the glass or plastic bends light compared to air, while R₁ and R₂ are the signed radii of curvature of the front and back surfaces; together they determine the focal length f and, as its reciprocal, the optical power in diopters.

Lens designers use this relationship to shape eyeglass lenses, camera and telescope objectives, and microscope optics before ever grinding glass, since it predicts focal length directly from geometry and material. Optical engineers, opticians fitting prescriptions, photography and telescope hobbyists, and physics students studying geometric optics all rely on it to size a lens for a target focal length or check how a given curvature and material will perform.