Frame Index Size Guide & Eyeglass Frame Calculator | Optical Fit Tool

Frame Index Size Guide

Discover how to measure, calculate, and compare eyeglass frame sizes using the Frame Index — a simple and reliable way to understand the true scale of any eyewear design.

Frame Size Calculator

🔍 What is Frame Index?

Frame Index is a numerical indicator that represents the overall dimensional balance of an eyeglass frame. It combines lens width, bridge width, and temple length into a single averaged value, allowing users and designers to compare frames quickly and consistently.

📏 Calculation Formula

Frame Index = (Lens Width + Bridge Width + Temple Length) ÷ 3

Example: (52 + 18 + 140) ÷ 3 = 70 → equivalent to a Medium Frame when adjusted for typical adult proportions.

📊 Frame Index Range Reference

CategoryFrame Index (mm)Front Width (A + DBL)Common Fit
Small≤ 130≤ 128 mmPetite / Female / Teen
Medium131 – 138129 – 136 mmAverage face
Large139 – 146137 – 144 mmBroad face / Male
Extra Large≥ 147≥ 145 mmOversized / Statement frame

Regional & Demographic Adjustments

Profile TypeAdjustment (mm)Typical Range
Asian Female-2 to -3128 – 136 mm
Asian Male-1 to -2130 – 138 mm
Western Female+1 to +2132 – 140 mm
Western Male+3 to +5135 – 145 mm
Child / Teen-10 to -15115 – 130 mm

Try the Frame Index Calculator

Enter your frame measurements and find out its size category instantly.

Result

Frame Index: —

Category: —

Unit: mm

⚙️ Other Frame Size Evaluation Methods

💡 Tip:

Frame Index is not an ISO standard but a widely used design reference. By applying consistent measurement logic, eyewear brands can provide better fit recommendations and unified size labeling.

Frame Size Eyewear Tool