How should sunglasses fit? The six-point check an optician does in thirty seconds

A pair of sunglasses fits when it sits level, touches your head in exactly three places, clears your brow and cheeks, and stays put when you look at your feet. That is the whole test, and it takes about thirty seconds. Most people never run it, buy on looks alone, and then spend a year pushing a frame back up their nose.

Here is the check in the order an optician would do it, with what each failure actually means.

Why three points of contact

A well-fitted frame rests on the bridge of your nose and lightly behind each ear. Those three points carry the weight and nothing else touches.

That matters because any fourth contact point is a pressure point. A frame resting on your cheeks will smear every time you smile. A frame gripping your temples will ache within an hour. A frame whose arms press hard behind the ears leaves marks and gives some people a headache — we cover that in why do sunglasses give me a headache.

Three points, evenly loaded. Everything below is a way of checking one of them.

1. Is it level?

Put the pair on, look straight into a mirror, and look at the top rim as a line across your face.

It should be horizontal, and it should sit roughly parallel to your brow line. A frame tilted a few degrees is the single most common fit fault and the easiest to fix — it almost always means one arm has been bent slightly out of shape, usually by being taken off one-handed for months.

Fix: most frames can be gently re-bent at the hinge or along the arm. Warm the arm slightly with a hairdryer if it is acetate; adjust cold if it is metal or TR90. Go in small increments.

2. Is it wide enough?

Look at where the outer edge of each lens sits relative to the widest part of your face — usually your cheekbones.

The frame should be as wide as your face at that point, or a few millimetres wider. Not narrower.

This is the one fault you usually cannot fix. If the frame is too narrow, the arms have to splay outward to reach your ears, which means they grip your temples and push the frame forward and down all day. No amount of adjustment creates width that is not there.

Too wide is a milder problem: the frame slides because nothing holds it, and it looks oversized. But it is still a reason to pick another pair.

Our measurements guide explains which of the three numbers printed inside the arm actually decides this. The short version: the lens width is the number people look at, and the one that matters is the total across the front.

3. Do the arms run straight back?

Take the frame off and look at it from above, lenses facing away.

The arms should run roughly parallel, or converge very slightly. If they bow outward in a V, the frame has been stretched by a face wider than it was built for — or it was always too narrow.

This is the physical cause of the slipping problem most people blame on weight or sweat. Splayed arms cannot grip. Our piece on sunglasses that keep slipping down your nose goes through the three causes and the fix for each.

4. Does the lens clear your brow and your cheeks?

Two checks, one at the top and one at the bottom.

Top: the upper rim should sit below your eyebrow, or just at it, without touching. A frame resting on your brow is too tall for your face and will be pushed off-level every time you raise your eyebrows.

Bottom: smile properly — a real one, not a polite one. Your cheeks rise. The lenses should not touch them. If they do, you will have smeared lenses permanently and the frame will be pushed upward every time your face moves.

Cheek contact usually means the frame is too deep (tall lenses) or the bridge is sitting too low on your nose.

5. The look-down test

This is the one that catches what a mirror will not.

Put the pair on, then look down hard at your own feet and hold it for a couple of seconds.

A properly fitted frame moves a little and stops. A badly fitted one slides down your nose, sometimes all the way off. If it slides, the frame is not being held by the three contact points — either the bridge is too wide for your nose, or the arms are not gripping behind the ears.

Do the same test with a brisk shake of the head side to side. Same standard: a little movement, then settled.

6. How does it feel after twenty minutes?

Fit faults that pass every visual check still show up as discomfort, and twenty minutes is usually enough to reveal them.

Pressure on the bridge of the nose that leaves deep red marks means the weight is concentrated too narrowly. On a frame with adjustable pads, widen them slightly. On a moulded bridge, it may just be the wrong frame — see our piece on low nose bridge fit if the pair sits too low generally.

Aching behind the ears means the arms are too tight or bent down too sharply.

A dull ache at the temples means the frame is too narrow and gripping the sides of your head.

What a professional adjustment can and cannot fix

Worth knowing before you give up on a pair you like.

Usually adjustable: tilt, arm angle behind the ear, nose pad width and angle on metal frames, slight overall width on acetate (with heat), the bend of the arm along its length.

Usually not adjustable: total frame width, lens depth, bridge width on a moulded one-piece frame, the basic curve of the front.

So if a pair fails checks 1, 3, 5 or 6, it is probably rescuable. If it fails check 2 or the cheek half of check 4, you are usually better off with a different frame.

Most opticians will adjust a frame you did not buy from them, often for nothing. It is worth asking.

The numbers, if you want them

If you prefer to shop by measurement rather than trial, three numbers are printed on the inside of almost every arm — something like 60-15-145.

• 60 — lens width in millimetres
• 15 — bridge width, the gap between the lenses
• 145 — arm length from hinge to tip

The useful comparison is against a pair you already own that fits. Measure or read those numbers off the good pair and look for something close. That is far more reliable than trying to translate your face into numbers — though if you want to try, our how to measure your face piece walks through it.

Our own T01 runs 60-15-145 with a 140mm front width, and the fit guide explains where those figures come from and who the frame suits.

Wrap frames change two of the checks

Worth a note, because sports and wrap frames fail two of the checks above while fitting perfectly well.

A wrap frame curves around the face, which means the arms are not straight and are not meant to be, and the lenses sit much closer to your cheeks than a flat frame would. Judged by the standard checks, a good wrap frame looks like it is failing.

The adjusted tests: the frame should still be level, should still hold through the look-down test, and the lenses should still clear your cheeks when you smile — but the margin will be smaller and that is by design. What you gain is coverage, which is the thing that actually blocks light arriving from the side, and which matters on water, snow and any reflective surface.

Fit changes with the frame's age

One last point people rarely connect.

A frame that fitted perfectly a year ago may not now. Acetate takes a set, hinges loosen, and arms splay from being pushed onto your head. The drift is gradual enough that you adapt to it rather than noticing it.

Re-run the six checks once a year, or any time a pair starts sliding when it did not before. Most of what you find is adjustable in a few minutes, and our how to fix loose sunglasses piece covers doing it yourself.

Frequently asked questions

The short version

Level. Three contact points. As wide as your face. Clear of brow and cheeks. Stays put when you look down. Comfortable after twenty minutes.

Run those six and you will know in half a minute whether a pair is worth buying — and if it fails, which failures a five-minute adjustment can fix and which mean you should put it back.