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Lens Thickness Calculator

Estimate how thick your eyeglass lenses will be based on your prescription and lens index. Compare different lens materials to find the best option.

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Quick Tip

Higher index = thinner lens. For prescriptions under ±2.00, standard 1.50 index is fine. For ±2.00 to ±4.00, consider 1.60. For ±4.00+, choose 1.67 or 1.74 for noticeably thinner lenses.

📋 Your Prescription

Negative (-) for nearsighted, Positive (+) for farsighted

Astigmatism correction (usually negative)

🖼️ Frame Size

52 mm
40mm (Small)60mm (Large)

Average: 63mm for adults (range: 54-74mm)

🔍 Lens Index

Edge Thickness (thickest point)

0.0 mm

with 1.60 index lens

Center Thickness

0.0 mm

Edge Thickness

0.0 mm

📊 All Index Comparison

💡 Recommendation

For your prescription of -4.00, we recommend 1.60 index lenses.

📋 Recommended Lens Index by Prescription

Prescription RangeRecommended IndexNotes
0 to ±2.001.50Standard plastic is sufficient
±2.00 to ±4.001.56 - 1.60Mid-index for better aesthetics
±4.00 to ±6.001.60 - 1.67High-index recommended
±6.00 to ±8.001.67 - 1.74High-index strongly recommended
±8.00+1.74Ultra high-index essential

🔍 Lens Material Comparison

IndexMaterialThicknessWeightPriceBest For
1.50CR-39 PlasticThickestHeavy$Low prescriptions (±0-2.00)
1.53TrivexThickLight$$Kids, sports, safety
1.59PolycarbonateMediumLight$$Impact resistance, kids
1.60MR-8ThinMedium$$$Moderate prescriptions (±2-4.00)
1.67MR-7Very ThinLight$$$$High prescriptions (±4-6.00)
1.74MR-174ThinnestLightest$$$$$Very high prescriptions (±6.00+)

🔬 How Lens Thickness Is Calculated

1

Prescription Strength

Higher prescription = thicker lens. A -6.00 lens is much thicker than a -2.00 lens.

2

Lens Diameter (Frame Size)

Larger frames require larger lenses, which exponentially increases thickness. Smaller frames = thinner lenses.

3

Refractive Index

Higher index materials bend light more efficiently, requiring less material to achieve the same power.

4

PD & Decentration

If your PD is narrower than the frame, the optical center shifts inward, effectively increasing lens diameter needed.

✅ Tips for Thinner Lenses

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Choose Smaller Frames — Frame size has the biggest impact on edge thickness
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Pick Round or Oval Shapes — Less edge exposure than rectangular frames
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Select Full-Rim Frames — Hides edge thickness better than rimless
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Center the Lenses Well — Proper PD alignment reduces decentration
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Consider Aspheric Design — Flatter curves reduce thickness further

💡 Key Facts

  • 1.74 index is ~50% thinner than 1.50
  • Minus lenses are thickest at edges
  • Plus lenses are thickest at center
  • Frame size matters as much as index
  • High-index lenses need AR coating

⚠️ Note

This calculator provides estimates. Actual thickness may vary based on lens design (aspheric, progressive), base curve, and manufacturing. Consult your optician for precise measurements.

Frequently Asked Questions

Your lens thickness depends on your prescription strength, frame size, and lens material (index). For prescriptions under ±2.00, standard 1.50 index is fine. For ±2.00 to ±4.00, consider 1.60 index. For stronger prescriptions above ±4.00, high-index lenses (1.67 or 1.74) are recommended to keep lenses thin and lightweight.

Lens thickness is calculated using the Sagitta (Sag) formula: Sag = (r² × Power) / (2000 × (n-1)), where r is the lens radius, Power is your prescription in diopters, and n is the refractive index. For minus (nearsighted) lenses, edge thickness = center thickness + sag. For plus (farsighted) lenses, center thickness = edge thickness + sag.

1.74 lenses are thinner than 1.67, but both are excellent choices for high prescriptions. 1.74 is best for prescriptions above ±6.00 where maximum thinness is desired. However, 1.67 offers better value and similar results for prescriptions between ±4.00 and ±6.00. 1.74 lenses are also more fragile and reflect slightly more light.

The thickness depends on your prescription and frame size. For example, a -4.00 prescription in a 50mm wide frame would be approximately 4.1mm at the edge with 1.67 index, compared to 5.5mm with standard 1.50 index. That's about 25% thinner. The higher your prescription, the more dramatic the difference.

The 1.74 index lens is the thinnest option available for high prescriptions. It can reduce edge thickness by up to 50% compared to standard 1.50 lenses. For extremely high prescriptions (±10.00+), combining 1.74 index with aspheric design and a small frame provides the thinnest possible result.

Yes, significantly! A larger frame requires a larger lens diameter, which dramatically increases edge thickness for minus lenses. Choosing a smaller, rounder frame can reduce edge thickness by 30-40%. For high prescriptions, frame selection is as important as lens index choice.

For prescriptions above ±3.00, high-index lenses are usually worth the extra cost. Benefits include: thinner and lighter lenses, better appearance (no 'coke bottle' look), more frame options, and improved comfort. The stronger your prescription, the more value you get from high-index lenses.

👓 Disclaimer: This calculator provides estimates based on standard optical formulas. Actual lens thickness may vary depending on lens design, base curve, and manufacturing specifications. Always consult a licensed optician for accurate measurements and recommendations.