A pair of glasses can look perfect on screen, then feel too narrow at the temples or slide down your nose once it arrives. Knowing how to read frame measurements takes much of the guesswork out of buying glasses online, especially when you are choosing a distinctive vintage or pre-loved designer frame.
The useful numbers are usually printed inside one of the arms. They are measured in millimetres and often look something like this: 52□18 140. Once you know what each number means, you can compare a frame with a pair you already wear comfortably and shop with far more confidence.
How to read frame measurements on your glasses
Most glasses measurements appear in a sequence of three numbers. The first is the lens width, the second is the bridge width, and the third is the temple length. You may see a small square, a dash or a gap between the first two numbers. That symbol simply separates the lens and bridge measurements.
Take 52□18 140 as an example. The frame has lenses that are 52mm wide, an 18mm bridge that sits across the nose, and 140mm arms that run from the hinge to behind the ear.
These figures are a helpful starting point, but they are not a guarantee that every frame with the same numbers will feel identical. Frame shape, material, nose pads and the overall width all affect the fit. A slim metal frame and a chunky acetate frame can share the same printed measurements yet sit very differently on the face.
Lens width: the first number
The first number, usually between about 45mm and 58mm for adult frames, is the horizontal width of one lens at its widest point. In the example above, 52 means each lens is 52mm wide.
Lens width gives a useful indication of the scale of the frame. Smaller numbers often suit narrower faces or a more compact look, while larger numbers usually create a broader, bolder appearance. But lens shape matters just as much. A 52mm round frame can look and feel quite different from a 52mm rectangular one, because the outer edges, height and curve are not the same.
If you like a statement oversized style, do not rely on lens width alone. Check the product photographs and, where provided, the full frame width. Oversized frames often have wider lenses, but a deep square shape can also give that fashion-led look without an especially large lens-width number.
Bridge width: the second number
The number after the square symbol is the bridge width. This is the distance between the two lenses, where the frame rests on your nose. In 52□18, the bridge is 18mm wide.
A bridge that is too narrow may pinch or sit too high. One that is too wide can allow the frame to slip, particularly if you have a narrower nose bridge. That said, fit is not as simple as choosing the same bridge number every time. Plastic frames have a fixed moulded bridge, while metal frames with adjustable nose pads can often be altered by an optician for a more secure fit.
For this reason, the bridge measurement is especially useful when comparing acetate or plastic frames with a pair you already own. If your current fixed-bridge glasses fit well, choosing a similar bridge size is a sensible way to narrow your options.
Temple length: the third number
The final number is the temple length, sometimes called arm length. It is usually 135mm, 140mm or 145mm. In the example, 140 means the arms measure 140mm from the hinge to the curved end behind the ear.
Temple length helps the glasses stay in place comfortably. Arms that are too short can press behind the ears or pull the frame forward. Arms that are too long may not hold the frame securely without adjustment. Most adults are comfortable in the 135mm to 145mm range, so a difference of 5mm is rarely dramatic, but it can matter if you already know you need a shorter or longer fit.
Vintage frames may occasionally have an older sizing format, or faded markings that are harder to read. When measurements are not printed clearly, a careful listing should provide the key dimensions separately.
The measurement that is often missing: total frame width
The three printed numbers do not tell you everything. Total frame width, measured from one outer edge of the frame front to the other, is one of the best indicators of whether glasses will feel narrow, standard or wide across your face. Yet it is not always stamped inside the arm.
This matters because hinges, lens shape and frame thickness add width beyond the lens measurement. Two frames marked 52□18 can have different total widths depending on their design. A thick retro acetate frame may extend farther at the outer corners than a fine wire frame with the same lens and bridge sizes.
When shopping online, compare the stated total width with your current favourite pair if you can. Lay your glasses flat, measure straight across the front at its widest point, and use that as a useful reference. There is no universal perfect number, but matching a pair that already feels comfortable is more reliable than choosing by small, medium or large alone.
Find your best size from a pair you own
The easiest way to buy a new-to-you frame is to start with the glasses you wear most. Look inside the arm for the three numbers, then note how the frame feels after a full day.
If it is comfortable across the nose and temples, use those measurements as your benchmark. You do not need an exact match. A lens width within 1-2mm and a similar bridge width will usually put you in the right area, while a 5mm difference in temple length can be manageable. The closer the frame shape is to your current pair, the more meaningful that comparison becomes.
If your glasses are always sliding, do not simply choose a smaller frame. The issue may be the bridge shape, worn nose pads or arms that need adjusting. An optician can often make minor fit adjustments, particularly to metal frames and nose pads, after you receive them.
Frame size and prescription needs
Your prescription can influence which frame shapes work best. Stronger prescriptions often suit smaller lens sizes because this can reduce lens thickness and weight around the edges. This is not a rule that prevents you wearing larger frames, but it is worth discussing with your optician before ordering lenses for a very wide or deep style.
Progressive or varifocal lenses also need enough lens depth to position the different viewing areas comfortably. A shallow, narrow vintage frame may be stylish, but may not provide the ideal space for every prescription. Check with your optician if you are unsure, particularly before choosing a very small retro design.
For single-vision lenses, you generally have more freedom. The priorities are a stable fit, suitable lens shape and a frame you will enjoy wearing every day.
A quick fit check before you choose
Measurements help you shortlist, then the design details help you decide. Look at the bridge style, the height of the lenses, the curve of the arms and the frame’s overall silhouette. A frame should sit comfortably without pressing at the temples, while your eyes should appear reasonably centred within the lenses rather than very close to one edge.
Pre-loved frames also deserve a closer look at condition. Check the listing for clear notes on any signs of wear, hinge condition and grading. At Maryten, frames are selected, inspected and cleaned before sale, so you can focus on finding a genuine designer style that suits both your face and your budget.
A little flexibility is useful when shopping for vintage eyewear. You may find that a frame with slightly different numbers gives you a better look than an exact match, and a straightforward optician adjustment can make a good fit even better.
The best measurement is ultimately the one that helps you feel comfortable enough to forget you are wearing your glasses. Start with the pair that already works for you, compare the numbers, then choose the frame that feels like your style.
