You know the pair that looked perfect on the model and turned you into a startled owl in the shop mirror? It wasn't the sunglasses. It was the shape.

A round face looks rounder behind round lenses. An oval face can wear almost anything (mildly unfair on the rest of us). And a square jaw goes from severe to cinematic behind a pair of aviators.

The rule is the same every time: pick frames that contrast with your face. Curves for angles, angles for curves, depth for length. Find your shape below and you'll know the three frames to try and the one to leave on the rack.

Every pair under each shape comes from our guides to the best sunglasses for men and the best sunglasses for women.

How do I find my face shape?

Pull your hair back, stand square to a mirror and compare two lines: the length from hairline to chin, and the width across your cheekbones. Then look at your jaw. Is it pointed, soft or square? Those three answers place you in one of the five shapes below. (The same five shapes decide which haircut suits you, too.)

If you land between two, pick the one your jaw agrees with. And if you can't decide, choose "Not sure" in the Personal Shopper at the top of this page and we'll match on your look instead.

Sunglasses for an oval face

Almost every frame suits an oval face. Your face is longer than it is wide, with balanced features and a gently curved forehead and chin, so no single line needs correcting.

That makes an oval face the one place to play. A square frame brings out your angles, a round frame softens them, and an aviator is somewhere in between. Treat it as an excuse to own more than one pair.

The one thing to skip is a frame wider than the widest part of your face. Oversized is fine; overhanging is not.

Sunglasses for a round face

Angular frames suit a round face best: rectangles, squares, wayfarers and cat eyes. Your face is about as wide as it is long, with a soft jaw, full cheeks and your cheekbones as its widest point. A frame with straight lines and corners adds the definition the face doesn't have.

A cat eye works too. Its upswept corners add the angles a round face lacks.

Skip round frames. A circle on a circle repeats the roundness instead of balancing it.

Sunglasses for a square face

Curves are the answer for a square face: round, oval, aviator and browline frames. You have a strong jaw and a broad forehead, and the face is close to as wide as it is long. A rounded lens softens all those corners.

The aviator is the classic fix. Its teardrop lens is wider at the top and curves in toward the cheek. That curve takes the edge off a hard jaw. Randolph has made aviators for the US military and still handcrafts every pair in Massachusetts. It's the one brand on this page we've tested ourselves, and our Randolph review covers how they wear.

Skip square, boxy frames. They trace the jawline you're trying to soften.

Sunglasses for a heart-shaped face

Aviators, cat eyes, round frames and rimless frames suit a heart-shaped face. Your forehead is the widest part of your face and it tapers to a narrow chin. A frame that keeps the brow light, or carries its weight lower down, evens out the two halves.

That's why rimless frames work so well here: with no heavy line across the top, nothing adds width where you already have it. A slim aviator does the same job with a little more presence.

Skip heavy, decorated brow lines. They add width where you have the most of it.

Cartier C Décor

Rimless gradient lenses on fine gold temples, about as light as gold sunglasses get. With no heavy line across the brow, it keeps a heart-shaped face in balance.

Check price: Cartier C Décor at Mytheresa

Sunglasses for a long face

Deep, wide and oversized frames suit a long face, and square and wayfarer shapes work too. Your face is clearly longer than it is wide, often with a high forehead. A frame with height and width breaks up that length and makes the face look shorter.

Go bigger than you think. A deep lens covers more of the face, and a thick frame with straight lines adds the width a long face lacks.

Skip small, narrow frames. On a long face they look like a postage stamp on a parcel.

Sunglasses questions, answered

How do I know which sunglasses suit my face?

Find your face shape in a mirror, then choose frames that contrast with it. Angular frames suit round faces, rounded frames suit square ones, and deep or oversized frames suit long faces. Oval faces can wear nearly anything. The Personal Shopper at the top of this page does the matching for you.

What should I avoid when buying sunglasses?

Avoid lenses without 100% UV or UV400 protection, and a frame that reaches past your temples. Don't assume darker lenses protect you better, because they don't. Check the fit too: the brow line should follow your eyebrows rather than sit above them, and your eyes should be at the center of the lens.

Can AI tell me what sunglasses look good on me?

It can narrow the field. Our Personal Shopper takes your face shape, your look and your budget and picks from the sunglasses in our guides, with three alternatives in case the first isn't you. A mirror still has the final word, so try the pair on before you commit.

Do polarized sunglasses protect against UV?

Not on their own. Polarized lenses cut glare off roads, water and snow. That makes bright days easier on the eyes. UV protection is a separate feature, so look for 100% UV or UV400 on the label. Our guide to the types of sunglasses explains the rest.

Compiled by Luxe Digital from our sunglasses guides and hands-on reviews.