Choosing eyeglass frames online is easier when you know how to read the numbers printed inside the temple. This guide explains lens width, bridge width, temple length, and total frame width, then turns those measurements into a practical checklist for comparing replacements and troubleshooting fit.
Overview
Most eyeglass frames show three numbers in a sequence such as 52-18-140. These are usually the lens width, bridge width, and temple length, measured in millimetres:
- Lens width: the horizontal width of one lens opening.
- Bridge width: the distance between the two lens openings at the nose.
- Temple length: the length of one arm, measured from the hinge toward the ear.
The first two numbers describe the front of the frame, while the third helps indicate how the temples reach behind your ears. The numbers are useful, but they are not a complete fit guarantee. Frame shape, lens height, bridge design, hinge placement, and material can all change how the same nominal size feels.
A frame marked 52-18-140, for example, has a 52 mm lens width, an 18 mm bridge, and 140 mm temples. The first two measurements are sometimes called the eye and bridge sizes. They may appear on the inside of a temple, although markings can be faint or absent on some frames.
To estimate the front size, add twice the lens width to the bridge width. In this example, 52 + 52 + 18 equals approximately 122 mm. This is a useful comparison point, but it is not always the same as the frame’s outside width. The rims, end pieces, hinges, and frame shape add material beyond the lens openings. When a retailer lists total frame width, use that measurement in preference to a calculation.
For online shopping, the best starting point is a pair you already wear comfortably. Read its markings, measure its actual width, and compare those details with the new frame’s product measurements. If your current glasses slide, pinch, or sit unevenly, do not copy every measurement automatically; identify the problem first.
Checklist by scenario
Replacing a comfortable pair
- Check the inside of both temples for the three-number size.
- Measure the full front width of the glasses with a ruler or millimetre measurement tool. Measure from the widest point, without stretching or bending the frame.
- Record the lens width, bridge width, temple length, and total frame width.
- Compare the replacement’s published measurements, prioritising total frame width and bridge design.
- Look for a similar lens height and overall shape if your current pair gives you good vision and coverage.
A replacement does not need to match every number exactly. A small change may work well when the frame shape and bridge are similar. Larger changes in width or bridge design deserve closer attention, especially if you use progressive lenses or have a strong prescription.
Buying prescription glasses online for the first time
- Measure a pair that fits, even if it is not your favourite style.
- Confirm the retailer lists the frame’s total width or provides a clear size guide.
- Check whether the bridge is a conventional nose bridge, a keyhole design, or an adjustable nose-pad system.
- Review the frame’s lens shape and height, not just its width.
- Keep your prescription and pupillary distance information ready. Frame measurements do not replace prescription details or PD measurement.
- Read the available fitting and return information before ordering.
For a broader preparation list, see our step-by-step guide to buying prescription glasses online and the online glasses buying checklist.
Choosing between narrow, medium, and wide frames
Use total frame width as the primary comparison when a retailer provides it. As a general starting point, the frame should sit comfortably across your face without pressing at the temples or extending so far that it looks unstable. The eyes should appear reasonably centred in the lens openings, although personal style and frame shape affect this.
A narrower frame can be appropriate when your current glasses leave noticeable space at the sides. A wider frame may be more comfortable when the temples press into your head or the front feels tight. Do not size up merely to create larger lenses: an oversized front can slide, shift your optical centres, and feel heavy.
Troubleshooting an existing fit
- Frames slide down: the bridge may be too wide or the temples may be too long or loosely adjusted. Nose pads and professional adjustment may help, but a poor basic size may continue to cause problems.
- Temples pinch: the front may be too narrow, or the temple arms may be pressing at the hinge or behind the ears.
- The bridge leaves marks: the bridge may be too narrow, the frame may be heavy, or the nose-pad position may need adjustment.
- One side sits higher: the frame may be twisted, your ears may sit at slightly different heights, or the frame may need adjustment.
- Eyelashes touch the lenses: the frame may sit too close to the face, or the bridge and nose-pad configuration may not suit you.
Persistent discomfort is a reason to seek an optician’s fitting help rather than repeatedly changing measurements at random. For style-related choices, our guide to choosing glasses for your face shape and features can be used alongside, not instead of, fit measurements.
Frame-measurement reference table
| Measurement | What it describes | How to use it online |
|---|---|---|
| Lens width | Width of one lens opening | Compare with a comfortable pair, while considering lens shape |
| Bridge width | Space between the lens openings | Check whether the frame will rest securely without pinching |
| Temple length | Length of each arm to the ear | Use as a guide, but also compare hinge position and temple shape |
| Total frame width | Outside width of the frame front | Usually the most direct size comparison for online shopping |
| Lens height | Vertical height of the lens opening | Important for coverage, appearance, and some multifocal designs |
Measurements can vary slightly by manufacturer and by the way a frame is measured. Treat them as a comparison tool rather than a promise of identical fit.
What to double-check
Bridge construction matters. Two frames with the same bridge number may feel different if one has a broad fixed bridge and the other uses adjustable nose pads. Acetate frames often have a moulded bridge, while many metal eyeglass frames use nose pads that can be adjusted by an optical professional. The listed number alone cannot describe every contact point.
Lens height matters. A frame can be wide enough yet still look or feel wrong if the lenses are much taller or shorter than your current pair. Lens height is especially worth checking when changing from a shallow rectangular frame to a round, cat-eye, or oversized shape. If you are considering progressive lenses, frame height and the fitting position should be discussed with the optician or retailer before ordering. Our comparison of progressive, bifocal, and single-vision lenses explains how lens type relates to everyday use.
Optical centres are separate from frame size. Your pupillary distance helps position the prescription correctly; it does not tell you whether the frame is physically comfortable. If a retailer requests single-eye PD measurements, enter them exactly as provided rather than guessing from a total PD.
Prescription strength can affect the best frame choice. Lens thickness, weight, and edge visibility may influence whether a smaller or more rounded frame is practical. High index lenses and coatings are separate decisions from frame measurements. You can review the trade-offs in our guide to eyeglass lens coatings.
Common mistakes
- Choosing only by the first number: lens width does not reveal bridge fit, total width, or temple placement.
- Assuming larger means more comfortable: an oversized frame can slide and may place the eyes away from the intended optical centres.
- Measuring a bent pair: worn or twisted glasses can produce misleading measurements. Use a pair that sits straight, or have it checked before copying its size.
- Ignoring the frame front: temple length cannot compensate for a front that is too narrow or too wide.
- Confusing style width with fit width: a bold rim may make a frame look larger without increasing the lens opening, while a thin rim may make it look smaller.
- Ordering without checking the product page: verify whether measurements refer to the finished frame, lens openings, or a general size category.
- Trying to fix every problem with home adjustments: twisting temples or heating plastic frames can damage them. Professional fitting is safer.
When to revisit your measurements
Return to this checklist whenever you replace glasses, change from small to oversized styles, move between acetate and metal frames, or notice slipping, pinching, unevenness, or eyelashes touching the lenses. Recheck measurements before seasonal shopping if your preferred retailer has changed its product pages or sizing labels, since presentation conventions can differ between collections.
Before placing an order, save a simple note with your comfortable pair’s lens width, bridge width, temple length, total front width, lens height, and the reason it fits well. Then compare the new frame in this order:
- Confirm the total frame width is close to your current pair or suits the fit change you intend to make.
- Compare the bridge design and width.
- Check lens height and shape.
- Review temple length, hinge position, and end-piece design.
- Verify your prescription, PD, lens type, and any desired coatings separately.
- Check fitting support and the retailer’s current return or exchange information.
Measurements narrow the options; comfort, optical accuracy, and a sound fitting process complete the decision. Keep this guide with your prescription details so the next time you replace your glasses, you can shop with a clear reference instead of starting from scratch.
