Lens Maker Equation Calculator

Written by Great Medico

Updated September 25, 2026 •2 min read

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The quickest way to trust a lens maker equation estimate is to see how the answer responds when an input changes. Optical calculations are unforgiving of unit and sign mistakes because wavelength, angle, focal length, and refractive index can change a result quickly. The sections below show what this page calculates, how it does it, and where the simplified model stops.

What this calculator does

This calculator isolates the relationship between Radius of curvature 1, Radius of curvature 2, Lens thickness and focal length. That makes it easier to see which input is controlling the result and to distinguish the headline quantity from secondary values shown underneath.

How to use it

For a clean calculation, enter Radius of curvature 1, Radius of curvature 2, Lens thickness, Refractive index exactly as defined by the labels and their units. Check the headline value, then scan the supporting metrics for a relationship that should obviously increase or decrease with one input; this is a fast way to catch an entry mistake.

How the calculation works

The page uses the thick-lens Lensmaker relation 1/f = (n−1)[1/R₁ − 1/R₂ + (n−1)d/(nR₁R₂)]. Curvature signs therefore matter. Once f is found, lens power is reported as 1/f in diopters when f is expressed in meters.

Example

Using the default example on the page (Radius of curvature 1 = 0.2 m; Radius of curvature 2 = -0.2 m; Lens thickness = 0 m; Refractive index = 1.5), the calculator returns focal length of 0.2 m. If a small input change sends the value in the opposite direction from the equation, recheck the selected unit and sign convention.

How to interpret the result

Read the focal length as the optical quantity defined by this page, not as a general rating of image or beam quality. Keep the displayed unit attached, and compare cases only after checking that angles, distances, wavelengths, and refractive indices use the same convention.

Limitations and notes

Real optical systems can add aberration, alignment error, finite bandwidth, diffraction, scattering, detector response, and component tolerances beyond the ideal relationship shown here. Before trusting the result, confirm Radius of curvature 1, Radius of curvature 2 and the associated units. This calculator does not replace component ratings, code requirements, or physical testing when those are required for a real design.