What Does 49 and 21 Mean on Optical Frames Size?
When you see numbers like 49□21 on eyewear, they represent key optical frame measurements.
49 = lens width optical frames (the width of one lens in millimeters)
21 = bridge width optical frames (the distance between the two lenses)
These numbers define the optical frame size, and the unit is millimeters (mm). They are usually printed on the inside of the temple. Sometimes, a third number is included, which refers to the temple length optical frames.
What Do the Numbers on Eye Glasses Mean?
There are typically two formats for optical frame sizes:
Two numbers (e.g., 49□21) → lens width + bridge width
Three numbers (e.g., 49□21–145) → lens width + bridge width + temple length
These values together form the standard optical frame measurements, helping users find the right fit.
What Is Lens Width in Optical Frames Size?
Lens width optical frames refers to the horizontal distance of one lens, measured from the far left edge to the far right edge in a straight line.
This is one of the most important parameters in optical frame size, as it affects:
the size of the lenses and overall width of the frame
What Is Bridge Width in Optical Frames?
Bridge width optical frames is the shortest distance between the two lenses, located at the nose bridge. This measurement determines how well the frame fits your nose:
Too wide → frames may slide down
Too narrow → pressure on the nose and discomfort
What Is Temple Length in Optical Frames Size?
Temple length optical frames refers to the length from the hinge to the end of the temple arm.
It affects how securely the glasses sit on your ears:
Too long → glasses may slip off
Too short → causes pressure and discomfort
For maximum comfort, all three optical frame sizes must work together.
How to Measure Optical Frames?
There are two main ways to check how to measure optical frames:
1. Check Frame Markings
Most frames have size information printed on the inside of the temples or bridge.
2. Measure Manually
If no size is marked, you can measure using a ruler:
Lens width: horizontal distance across one lens
Bridge width: narrowest distance between lenses
Temple length: hinge to the end of the temple
Relationship Between Frame Width and Face Width
The total width of optical frame sizes should match your face width or be slightly wider (within 2–3 mm).
Too wide → poor fit and unstable
Too narrow → uncomfortable and tight
Face width is usually measured across the cheekbones. Matching this with wide optical frames or big optical frames can improve comfort and appearance.
How to Measure Different Types of Optical Frames Size?
1. Round Optical Frames
For round optical frames or round metal optical frames, measure the widest horizontal point across the lens (not diagonally).
2. Square or Rectangular Optical Frames
For square optical frames or rectangular optical frames, measure the straight horizontal distance between the inner or outer edges.
3. Cat Eye Optical Frames
For cat eye optical frames, measure the widest horizontal distance. Note that the outer corners curve upward, but the widest point is usually lower.
4. Aviator Optical Frames
For aviator optical frames, measure across the widest lower section of the lens, keeping the ruler horizontal.
5. Polygon Optical Frames
For hexagonal or geometric frames, move the ruler horizontally at different heights to find the maximum width.
6. Half Rim Optical Frame
For a half rim optical frame, measure the actual lens area (not the upper frame only), using the same method as full-rim frames.
