Tortoise-toned eyeglasses and a metal measuring tool on textured stone in directional light.

How to Read Eyeglass Frame Sizes: What 52–18–140 Tells You

By Le Seven Optical

On a frame marked 52 □ 18 – 140, the numbers usually mean a 52 mm lens width, an 18 mm bridge measurement and a 140 mm temple length. Record all three, then compare overall frame width, lens height and bridge design. Matching the printed numbers is a useful starting point, but it cannot guarantee the same fit.

Pair the numbers with a visual reference

Frame measurements tell you about physical size; a reference image helps you picture the proportions. After you shortlist a size, filter Reference Looks by face width and compare real frames on a selected face. Keep the product measurements open as you narrow the choice.

What 52 □ 18 – 140 tells you

Look inside either arm of your glasses. The size may appear beside a model name or colour code. Copy the complete marking before deciding which digits describe the size; a model number can also contain three or four digits.

Read the three measurements in this order
Marking Meaning What to compare
52 Lens width, in millimetres One lens opening, excluding the surrounding rim
18 Bridge measurement, in millimetres The spacing between lenses; also examine the bridge and nose pads
140 Temple length, in millimetres The arm from hinge to tip, including the bend

The small square separates the first two values. Some frames use spaces or dashes, and some print only the lens and bridge values. Manufacturers use the same basic lens/bridge/temple sequence; see Ray-Ban’s explanation of frame markings.

Illustrative frame showing lens width, bridge spacing and a temple-length path that follows the arm from hinge to tip.
Each arrow has a different job. The example is an illustration, not a measurement of a Le Seven product.

Two useful measurements may be missing

Overall frame width describes the complete front, including its outer rim and endpieces. Lens height describes how tall the lens opening is. These add context that the printed sequence alone does not supply. Warby Parker’s measurement reference explains both.

Do not label 52 + 52 + 18 = 122 mm as the overall frame width. That sum does not include all of the outer frame construction. If a product page gives overall width, use that separately. If it does not, leave the value unknown and ask before relying on it.

Two hypothetical lens openings have equal 52 mm widths but heights of 34 mm and 44 mm, drawn at the same scale.
Illustrative comparison: the taller opening has the same width. Neither example is a product, a recommended size or a prediction of on-face fit.

Compare a candidate with your reference pair

Choose a pair you currently wear comfortably. If it slips, pinches or feels unstable, record that too: reproducing its numbers may reproduce a problem rather than solve it. Use the seven-point fit guide to organize what you notice.

  1. Record the reference. Write down the brand/model, complete size marking and what you like or dislike about the fit.
  2. Collect the candidate’s listed dimensions. Record each number under its own heading. Check that you are looking at the intended size and colour variant.
  3. Compare the construction. Look at the bridge, nose pads, rim thickness and side view. A shared bridge number does not make two bridge designs identical.
  4. List the unresolved questions. Ask for missing measurements rather than estimating millimetres from a product photograph. Perspective and crop make that unreliable.

For example, imagine your comfortable reference is marked 52 □ 18 – 140, while a candidate is 52 □ 18 – 145. Lens width and bridge marking match; the candidate’s listed arm length is 5 mm longer. You still need its overall width, lens height and bridge design to make a useful comparison. The extra 5 mm is a difference to investigate, not a verdict that it will fit better or worse.

If the marking has worn off

First check the original model listing or ask the retailer/manufacturer. If you make a home comparison, use a millimetre ruler and record exactly what you measured. Keep a ruler away from the lens surface to avoid scratching it.

You can note the widest horizontal span of a lens opening, its greatest vertical span, and the widest part of the complete front as separate approximate observations. Keep them labelled home measurements; they may differ from the manufacturer’s specifications. A straight hinge-to-tip shortcut misses a curved arm’s path. Do not bend or straighten the frame to measure it.

Make your own comparison sheet

Copy the table into a note, or open the printable worksheet. Write “unknown” where a value is missing. The worksheet is a record sheet, not a scale ruler or a sizing calculator.

Reference pair versus candidate
Record separately Reference pair Candidate
Model / size / colour ________ ________
Lens / bridge / temple (mm) ________ ________
Overall width / lens height (mm) ________ ________
Source: label, listing or home measurement ________ ________
Bridge design / fit notes ________ ________
Question to resolve before ordering ________________________________

Questions that commonly trip up a comparison

Is 52 a small, medium or large frame?

It describes one lens width. Use the particular brand’s size guidance and the complete frame dimensions rather than treating that single number as a universal size category.

Do these numbers tell me my PD?

No. Frame measurements describe the frame; pupillary distance describes your eyes. Do not use lens width plus bridge width as a substitute for your PD. Consult the PD guide or your eye-care professional when preparing an order.

Will matching all three numbers give me the same fit?

No. Matching markings do not establish identical overall width, bridge contact or proportions. Keep the reference useful by recording those differences too.

Can the worksheet confirm prescription compatibility?

No. It organizes frame information. Lens suitability and fitting requirements need confirmation for the actual frame, prescription and lens choice.

Take the comparison to the product page

Keep your reference notes beside you as you browse prescription frames. For shape ideas, compare the Round collection with the Oval collection, then check each candidate’s own specifications. The Le Seven size guide brings the main fitting references together.

Keep comparing

Back to blog