Tools

Calculate induced prism from decentration with Prentice’s rule. Enter lens power and decentration for the prism, or any two of prism, power and decentration to solve for the third.

Check a finished pair of glasses against ANSI Z80.1 in seconds. Enter the ordered prescription and the lensmeter reading, and the tool flags sphere, cylinder, axis and add as pass or fail against the standard.

This post presents the common method for estimating the minimum lens block diameter, also known as Minimum Blank Size (MBS), using the formula “Frame Bridge + Frame Width – PD + Longest Diagonal + 2 mm” widely adopted in labs and optical shops. Despite its simplicity, this method offers bench‑speed calculation and a safety margin for block cutting, though it can be imprecise for complex frame geometries.

Compensate lens power for a change in vertex distance. Enter the refracted power, the refraction vertex and the as-worn vertex, and the calculator returns the power to order. Matters above ±4.00 D.

Convert a spectacle prescription to the equivalent contact lens power. The tool applies the vertex formula, which matters above about ±4.00 D, and returns the power to order.

Convert a sphero-cylindrical prescription between plus-cylinder and minus-cylinder form. Enter sphere, cylinder and axis and the calculator returns the transposed Rx instantly, with the shared spherical equivalent.

Enter your prescription below to compare lens thickness and weight across seven refractive indices, from standard CR-39 to 1.74 ultra-thin. The calculator uses the sagitta formula and ANSI Z80.1-2025 minimum thicknesses to estimate edge thickness (minus lenses) or center thickness (plus lenses) for each material, so you can see exactly how much thinner and lighter each upgrade gets.