How to choose glasses frames

Look inside one temple of almost any pair of glasses and you will find three numbers, such as 52-18-140, sometimes with a small square between the first two. All three are in millimeters. The first is the lens width, measured across one lens at its widest point. The second is the bridge, the gap between the two lenses where the frame crosses your nose. The third is the temple length, from the hinge to the tip that curves behind your ear.

Lens width sets most of the frame size. Lens widths usually run from about 40 to 60 mm, and because there are two lenses, 2 mm more per lens makes the whole front 4 mm wider. Add both lens widths and the bridge and you get close to the width of the front; the rims and hinges add a few millimeters more.

The bridge decides where the frame sits on your nose. It usually measures between 14 and 24 mm. Too narrow, and the frame perches high and pinches; too wide, and it drops until the lenses sit low in front of your eyes. On frames with adjustable nose pads the printed bridge matters less, because the pads can be moved.

Temple length, usually between 120 and 150 mm, decides whether the arms reach behind your ears. Too short, and the tips press on the top of the ear; too long, and the bend sits behind the ear without holding anything, so the glasses slide. The easiest way to use all three numbers is to find them on a pair that already fits and stay within a couple of millimeters for lens and bridge, a little more for the temples.

Numbers get you close; the mirror settles it. Stand at arm's length in good light, look straight ahead and go through these checks, much as an optician does when you collect a new pair.

Eyes centered in the lens. Each pupil should sit near the middle of its lens from side to side, and at or slightly above the middle from top to bottom. If your eyes sit close to the inner edges, the frame is too wide for you; if they sit near the top rim, it is sitting too low.

Frame width at the temples. The front should end about where your face does at the temples, with the arms running straight back. Arms that bow outward mean the front is too narrow; a gap you can see between the arms and the sides of your head means it is too wide.

Brow line and cheeks. The top rim should follow your eyebrows rather than cut across them, and your brows should stay in view. Then smile broadly: the lower rim should not touch your cheeks, and your lashes should not touch the lenses when you blink.

Nose bridge and pads. The weight should rest evenly on both sides of your nose, with no gap under the bridge and no pinching. Acetate frames sit on a fixed, molded bridge that has to match your nose as it is, while metal frames sit on pads an optician can move. If acetate frames always slide on you or rest on your cheeks, look for a low bridge fit, which has built-up pads for a flatter nose bridge.

Temple ends behind the ears. The arms should bend down just behind the top of each ear and follow its curve without pressing. Nod and look down at the floor: if the glasses move, the bend sits too far back or the front is too wide.

Acetate is a plant-based plastic cut from thick sheets, which is why it comes in deep colors, layered tortoiseshell and clear tints. It feels solid, and an optician can warm it to reshape the temples and bridge. The trade-off is weight: a thick acetate front rests directly on the nose and weighs more than a metal one of the same size.

Metal frames, most often stainless steel or another alloy, give a thin, precise outline and sit on adjustable nose pads, which makes them easy to fit to a low or narrow bridge. Some alloys contain nickel, so if metal jewelry irritates your skin, say so before you choose.

Titanium is lighter than steel, very strong, and does not corrode with sweat. Pure titanium contains no nickel, which makes it the usual answer for sensitive skin, and titanium parts are what keep rimless glasses and many half-rim frames so light. It usually costs more than other metals.

Nylon-based plastics are light, flexible and hard to break, which is why sport frames and many children's frames use them. They bend back after a knock instead of snapping, but they keep their molded shape and give an optician less room to adjust them than acetate does.

Many frames mix materials: an acetate front with metal temples, or a metal chassis under an acetate brow, as on browline glasses. Mixing keeps the look of acetate where it shows and the lightness of metal where it does not.

Your prescription does not limit you to a handful of frames, but it makes some choices easier than others. Lenses for nearsightedness are thinnest in the middle and thickest at the edge; lenses for farsightedness are the other way around. In both cases a strong lens looks thinner in a smaller frame, because a smaller lens leaves less room for that thickness to build up.

Frame width matters too. A frame far wider than the span between your two pupils puts more lens on the outer side of each eye, and with a strong lens that is where the extra thickness shows. A full rim, especially in acetate, hides an edge that a thin metal rim or a rimless mount leaves on show. Small, round shapes such as round glasses are among the kindest to strong lenses.

Progressive lenses need height. The reading zone sits low in the lens, so a very shallow frame can squeeze it into a narrow band; ask your optician for the minimum lens height your lenses need before you settle on a slim pair. Strongly curved sport frames can also be hard to fit with a strong prescription.

Your optician has the final word on all of this. Take the frame you like, or its measurements, and ask whether it suits your prescription, which lens material they would use, and whether a high-index lens would keep it thinner.

Start with your skin's undertone. If gold jewelry flatters you more than silver, your undertone is probably warm, and tortoiseshell, honey, olive, warm browns and gold metal will suit you. If silver looks better, cool shades such as black, gray, navy, crystal, silver and gunmetal are the safer choice. Neutral undertones can wear either.

Then look at contrast. Dark hair with fair skin is high contrast and carries black frames and strong colors; light hair with light skin is low contrast and looks best in softer shades, such as light tortoiseshell, clear or champagne acetate, or thin metal. Gray and silver hair go well with silver, gunmetal and crystal, or with one clear color as an accent.

Your eyes and brows come last. A frame with flecks or a tint that picks up your eye color makes your eyes stand out, while a frame much darker than your brows draws a heavy second line above them. Since a frame sits on your face all day, choose a color that goes with most of your wardrobe and save bright colors for a second pair.

For work, most people want a frame they stop noticing: a calm shape such as a rectangle or an oval, a neutral color that goes with what you wear, and a fit firm enough for a long day. An anti-reflective coating stops the lenses flashing under office lights and on video calls.

If you spend hours at a screen, tell your optician how far away it sits. A screen is usually farther away than a book and closer than the street, and lenses made for that middle distance, or office lenses that cover both desk and room, may make long days easier than ordinary reading glasses. Those lenses need a frame with enough height, just as progressives do.

For sport, the frame has to stay on and survive a knock. Look for light, flexible nylon frames with rubber nose pads and temple tips that grip when you sweat, impact-resistant lenses such as polycarbonate, and a curved shape or a strap for fast sports. If you need your prescription in sport, check that the frame can carry it, either in the lenses or as an insert behind them.

One frame rarely does all of this well. A practical setup is an everyday pair chosen for fit and comfort, plus prescription sunglasses or sports glasses for the times your main pair is the wrong tool; sunglasses by face shape follow the same rules.

Work through the choice in this order and each step narrows the next. Write down the three numbers from a pair that fits. Shortlist two or three shapes using our face shape guide, then try them on your own photo to see which ones look like you.

Once you have a favorite, check its measurements against yours, decide on material and color, and take it to your optician with your prescription before you order. A frame that passes the mirror checks and your optician's is one you can stop thinking about.