The numbers printed inside an eyeglass temple usually show three basic measurements: lens width, bridge width, and temple length. For example, 52□18-145 normally means a 52 mm lens width, 18 mm bridge width, and 145 mm temple length. These numbers are useful, but they do not describe the complete fit of a frame. For eyewear buyers, total frame width, lens height, endpiece position, temple curve, bridge geometry, and production tolerances can also affect the final fit. This eyeglass frame size guide explains how to read, measure, and specify these dimensions when developing or sourcing eyewear.
What Do the Numbers on Eyeglasses Mean?
A typical size marking looks like:
52□18-145
The three numbers describe the basic dimensions of the frame.
| Marking | Measurement | Meaning |
|---|---|---|
| 52 mm | Lens width / eye size | Horizontal width of one lens |
| 18 mm | Bridge width / DBL | Distance between the two lens areas |
| 145 mm | Temple length | Nominal length of the temple |
The small square symbol between the first and second numbers is commonly used to separate the lens width and bridge width.
These measurements are generally expressed in millimeters (mm).
However, buyers should not use these three numbers as the complete technical specification of a frame. ISO 8624:2020 defines a measuring system and vocabulary for spectacle frames.
First Number: Lens Width / Eye Size
The first number represents the horizontal lens dimension.
For example:
52□18-145
means the nominal lens width is 52 mm.
This measurement is important when comparing frame proportions. A 52 mm lens in a narrow oval frame can look and fit very differently from a 52 mm lens in a wide rectangular frame.
Second Number: Bridge Width / DBL
The second number represents the bridge dimension, commonly called DBL (Distance Between Lenses).
In the example above:
18 mm = bridge width / DBL
The bridge affects how the frame sits around the nose and contributes to the overall front geometry.
For an OEM or ODM project, simply specifying “18 mm bridge” is not always enough. The bridge shape, height, curvature, nose-pad position, and front angle may also need to be confirmed.
Third Number: Temple Length
The third number represents the nominal temple length.
In:
52□18-145
the temple length is 145 mm.
This dimension provides a reference for how far the temple extends toward and around the ear. Actual wearing comfort also depends on the temple curve, bend position, thickness, and end-tip geometry.
How to Find Eyeglass Frame Size Information
There are several ways to obtain frame dimensions.
1. Check the Inside of the Temple
Look at the inner side of the temple. Many commercial frames have markings such as:
50□20-145
or
52-18-140
These markings normally provide lens width, bridge width, and temple length.
2. Check the Supplier Product Specification
For B2B sourcing, ask the supplier for a complete dimensional drawing rather than relying only on the printed temple numbers.
A useful specification can include:
- Lens width
- Lens height
- DBL / bridge width
- Total frame width
- Temple length
- Endpiece width
- Bridge height
- Temple opening
3. Measure a Physical Reference Frame
If you are developing a private-label product from an existing frame, send the physical reference sample to the manufacturer or measure it with a suitable tool.
For custom development, a physical sample is often more useful than a size marking alone because it allows the manufacturer to inspect the frame geometry.
4. Use the Manufacturer’s Technical Drawing
For a new mold or ODM development, dimensions should be transferred into a technical drawing or Tech Pack.
This creates a common reference for the buyer, designer, sample maker, and production team.
Detailed Eyeglass Frame Dimensions Explained
Lens Width
Lens width, also called eye size, is the horizontal dimension of one lens area.
It is normally measured across the lens opening or according to the applicable frame measuring system.
For example:
Lens width = 52 mm
does not mean that the entire front is 52 mm wide.
A frame with two 52 mm lenses can have a front width of more than 120 mm after the bridge and endpieces are included.
For B2B buyers, lens width should be considered together with lens height and total frame width.
Lens Height / B Measurement
Lens height is the vertical dimension of the lens opening.
It is sometimes called the B measurement in optical frame terminology.
Two frames can have the same 52 mm lens width but very different lens heights.
A 52 × 36 mm lens and a 52 × 44 mm lens do not create the same visual proportions or lens coverage.
For a manufacturer, lens height is also useful when confirming lens shape and frame construction.
Bridge Width
The bridge connects the two lens areas.
The printed bridge number is commonly referred to as the DBL.
For example:
52□18-145
has an 18 mm nominal bridge dimension.
However, bridge width alone does not determine nose fit.
You should also consider:
- Bridge shape
- Bridge height
- Nose-pad position
- Nose-pad size
- Front tilt
- Frame material
This is especially important when comparing acetate, PC, TR90, and metal frames.
A metal frame with adjustable nose pads can provide a different fit from an injection frame with an integrated bridge, even when both have similar nominal DBL dimensions.
Temple Length
Temple length is the nominal length of the temple.
Common commercial markings may include values such as:
135 mm, 140 mm, 145 mm or 150 mm.
But the number alone does not describe how the temple behaves on the head.
For a technical specification, also confirm:
- Temple length
- Temple thickness
- Temple width
- Hinge position
- Bend position
- Temple curve
- Ear-tip shape
- Opening angle
A temple that is nominally 140 mm can feel different from another 140 mm temple if the bend begins at a different position.
This is one reason physical sample approval remains important during eyewear development.
Total Frame Width
Total frame width describes the overall front width of the frame.
This is one of the most useful measurements for determining whether a frame is narrow, medium, or wide.
However, it is not simply the first number × 2 + the second number.
For example:
52 + 18 + 52 = 122 mm
is only a simple theoretical calculation.
The actual front width can differ because of:
- Lens shape
- Rim thickness
- Endpiece geometry
- Bridge construction
- Frame curvature
- Hinge structure
For product development, use the actual measured total frame width rather than calculating it from the printed size numbers.
Endpiece and Hinge Position
The endpiece is the area where the front frame connects to the temple and hinge assembly.
Its position affects the actual front width and temple geometry.
Two frames may have identical:
52□18-140
markings but different endpiece structures.
The differences can affect:
- Overall front width
- Temple spread
- Hinge alignment
- Face coverage
- Visual proportions
- Wearing position
When developing a new frame, the hinge location should therefore be included in the technical drawing.
This is particularly important when a buyer wants to reproduce the fit of an existing reference frame.
How to Measure Eyeglasses with a Millimeter Ruler or Caliper
A simple ruler can work for general comparison. A digital caliper is more useful when the measurement needs greater consistency.
Step 1: Place the Frame on a Flat Surface
Close both temples and place the frame front facing upward.
Make sure the frame is not twisted.
Step 2: Measure Lens Width
Measure horizontally across one lens opening.
Record the result in millimeters.
Example: 52.1 mm
Do not automatically round the result to 52 mm unless your specification requires a nominal size.
Step 3: Measure Lens Height
Measure vertically from the highest point of the lens opening to the lowest point.
Record the measurement separately from lens width.
Step 4: Measure Bridge / DBL
Measure the specified bridge dimension according to the chosen measurement system.
For production documents, use one consistent measuring method.
ISO 8624:2020 provides the formal measuring system and vocabulary for spectacle frames.
Step 5: Measure Total Frame Width
Measure across the front from the outermost relevant points.
Record exactly where the measurement begins and ends.
This matters because different teams may otherwise measure slightly different locations.
Step 6: Measure Temple Length
Measure the temple according to the manufacturer’s or technical drawing’s defined reference points.
Do not mix different measurement methods between suppliers.
Why Frames with the Same Printed Size Can Feel Different
This is a common issue for eyewear buyers.
A frame marked 52□18-145 is not guaranteed to feel identical to every other frame carrying the same numbers.
The reason is that the three printed numbers describe only part of the frame geometry.
Frame Shape
A round, oval, rectangular, and cat-eye frame can have the same lens width but very different visual and physical proportions.
Bridge Design
The bridge determines how the front sits around the nose.
A narrow bridge, high bridge, low bridge, integrated bridge, and adjustable nose-pad construction can produce different fitting results.
Endpiece Position
Moving the hinge and endpiece outward can change the effective front width and temple position.
Temple Curve
A straight 145 mm temple and a strongly curved 145 mm temple can sit differently behind the ears.
Material Flexibility
Material changes how the frame responds to the wearer’s head.
For example, acetate, TR90, PC, and metal have different structural characteristics and adjustment possibilities.
Nose Pads
Nose pads can change the vertical position and nose contact area.
This means that frame size is a dimensional reference, not a complete fit description.
For buyers, the best practice is to compare both the numbers and the physical sample.
Frame Size and Pupillary Distance Are Not the Same Measurement
Frame dimensions and PD (pupillary distance) describe different things.
Frame measurements describe the physical geometry of the eyewear.
PD describes the distance between the wearer’s pupils.
For example:
Frame: 52□18-145
PD: 64 mm
These numbers cannot be substituted for each other.
A frame with a 52 mm lens width does not mean that it is suitable for a person with a 52 mm PD.
For prescription eyewear, optical positioning requires consideration of the wearer’s measurements, lens design, frame geometry, and dispensing process.
For B2B buyers, this distinction is important when writing product specifications. Do not describe a frame’s eye size or DBL as a PD specification.
Common Eyeglass Frame Measurement Mistakes
Mistake 1: Confusing Lens Width with Total Frame Width
A 52 mm lens does not mean the frame is 52 mm wide.
The lens width refers to one lens area.
Total frame width includes the complete front geometry.
Mistake 2: Using Centimeters Instead of Millimeters
Eyewear frame specifications should normally be documented in millimeters.
Avoid writing:
5.2 cm × 1.8 cm × 14 cm
Use:
52 mm × 18 mm × 140 mm
This reduces confusion during technical communication and production.
Mistake 3: Not Confirming Tolerances
A nominal dimension is not the same as a production acceptance range.
If the buyer requires a specific size, define:
Nominal size + tolerance + measurement method.
This gives both sides a clear acceptance reference.
Mistake 4: Ignoring Temple Curvature
Two temples can have the same nominal length but different curves.
This can change the wearing position and perceived fit.
When approving a sample, inspect the temple from the side rather than checking only the number printed on it.
FAQ
1. Can I use the size of my current sunglasses to design an optical frame line?
No. Sunglasses generally utilize a larger lens width (54mm+) and a stronger base curve (Base 6) for sun protection. Optical frames require smaller lenses (48-52mm) and flatter curves (Base 4) to accommodate prescription lenses without distortion.
2. What is the most universally fitting frame size for a startup brand to launch with?
For an adult unisex market in Europe/US, a safe baseline is a total frame width of 136mm-140mm, featuring a 50mm lens, 20mm DBL, and 145mm temple.
3. How do I know the total width of an eyeglass frame?
Measure across the front at the defined outer reference points. Do not simply add the two lens widths and bridge because endpieces, lens shape, and frame geometry affect the actual width.
4. Is a larger lens width always a larger frame?
No. Lens width is only one dimension. Lens height, bridge width, endpiece position, and frame shape can make two frames with the same lens width feel very different.
Conclusion
Understanding eyeglass frame dimensions is important when comparing suppliers, developing private-label eyewear, or approving production samples. The familiar lens width–bridge–temple length marking is a useful starting point, but it is not a complete manufacturing specification.
For B2B eyewear projects, buyers should define the complete frame geometry, measurement references, tolerances, hinge position, lens fitting details, and sample requirements. This gives the manufacturer a clear technical target and makes sample-to-production comparison easier.
Jioneyewear supports OEM and ODM eyewear projects for emerging brands, including custom frame development, material selection, logo customization, packaging, samples, and production.
If you are preparing a custom eyewear project, please send us a reference frame or design drawings, target dimensions, material specifications, estimated quantities, and customization requirements. These details will provide a clearer basis for us to evaluate the project.
