Eyeglass Lens Thickness Calculator
This tool estimates the center and edge thickness of eyeglass lenses. Enter your prescription details and lens parameters to get an approximate calculation. Remember, this is an estimate; actual thickness may vary due to specific lens design, base curve, and manufacturing processes.
Enter your prescription and lens details below and click “Calculate Thickness”
Understanding Lens Thickness
The thickness of an eyeglass lens is determined by several key factors:
- Prescription Power (Sphere & Cylinder): Higher powers (further from zero, whether plus or minus) generally result in thicker lenses. Minus lenses are thinnest at the center and thickest at the edge. Plus lenses are thickest at the center and thinnest at the edge.
- Refractive Index (n): This measures how efficiently the material bends light. A higher refractive index means the lens can be made thinner for the same prescription power.
- Lens Diameter: Larger lenses will generally be thicker, especially for minus powers at the edge and plus powers at the center, assuming the same prescription. This is related to your frame size.
- Minimum Center/Edge Thickness: Lenses have minimum thickness requirements for safety and durability. For minus lenses, the center thickness is a key constraint. For plus lenses, a minimum edge thickness is usually maintained.
- Cylinder & Axis: Astigmatism correction (cylinder) means the lens has different powers in different meridians. This will cause the edge thickness (for minus lenses) or center thickness (for plus lenses) to vary around the lens periphery. This calculator provides an estimate, and the actual thickness will be most pronounced along one of the principal meridians.
- Base Curve & Lens Design: The front curve of the lens (base curve) and advanced lens designs (like aspheric or atoric surfaces) can also influence the final thickness and cosmetic appearance. These are not directly factored into this basic calculator.
This calculator uses a simplified formula (related to lens sagitta) to provide an estimate:
Sagitta (thickness change) ≈ (Power × Diameter²) / (2000 × (Refractive Index – 1))
The results show estimated Center Thickness (CT) and Edge Thickness (ET). For lenses with cylinder, the reported edge or center thickness typically refers to the thickest meridian.