Lens Thickness Calculator

Predict how thick your lenses will be before visiting the optician.

Use (-) for Nearsighted, (+) for Farsighted.
Usually found on the temple of your frames.
Standard safety minimum is 1.5mm - 2.0mm.

How Eyeglass Lens Thickness is Calculated

When ordering new glasses, especially with a high prescription, the most common concern is: "How thick will my lenses be?" Our professional calculator uses the Sagitta formula to provide an accurate estimate of your lens depth at both the center and the edges.

The Physics Behind the Calculation

The thickness of an optical lens is determined by the interaction between the lens power (SPH), the refractive index, and the frame diameter. We use the Sagitta formula:

Sagitta =
h2
2 ⋅ r

Where h is the radius of the lens and r is the radius of curvature.

Why Refractive Index Matters

The Refractive Index (e.g., 1.50, 1.67, 1.74) indicates how efficiently a material bends light. A higher index means the material is more "powerful" at bending light, allowing the lens to be significantly thinner and lighter.

  • 1.50 (Standard): Best for low prescriptions (below +/- 2.00).
  • 1.61 / 1.67 (High Index): Recommended for prescriptions between +/- 3.00 and +/- 6.00.
  • 1.74 (Ultra High Index): The thinnest plastic lens available, ideal for prescriptions above +/- 6.00.

3 Tips to Get Thinner Lenses

  1. Pick Smaller Frames: The "A-size" (width) of the frame is the biggest factor in edge thickness for minus lenses. Reducing frame width from 54mm to 50mm can have a bigger impact than upgrading the lens index.
  2. Choose Rounded Shapes: Lenses are thickest at the corners. Round or oval frames eliminate the thickest parts of the lens that would be present in rectangular frames.
  3. High-Index Materials: If you have a high negative SPH (nearsighted), always opt for 1.67 or 1.74 to avoid the "coke bottle" effect.
Note: This tool provides a mathematical estimate. Final thickness may vary depending on the specific frame shape (B-measurement), your Pupillary Distance (PD), and the lens laboratory's finishing techniques.