If you’re like many of us, you’ll spend more time in a t-shirt than in any other item of clothing (except your underwear, hopefully). In fact, the humble tee is so commonplace that the dark art of sizing doesn’t quite get the attention it deserves. Rather than bulk buying simple undershirts, try taking your time finding a t-shirt that fits, because there’s no simpler way to make your everyday look more fashionable.

It’s easy to see why t-shirts have become so popular. In the age of athleisure, comfort is king and formal clothes are becoming less and less common. There’s hardly a more comfortable garment than a well-fitted t-shirt, which is neither too tight nor too loose, without scratchy labels or irritating collars.

They’re also the most versatile of clothes. Some will only toddler tees for activities which demand no fashion—sport, sleeping, lounging around at home. But t-shirts are also an opportunity to show your interests to the world around you, whether you’re buying one or designing a custom t-shirt for your business, brand, event or group. If you show others what your favourite brand or movie is, you might find some new friends with something in common come and introduce themselves.

But just because they’re comfy and versatile, it doesn’t mean t-shirts can’t be fashionable. A solid-colour tee is a classier look, especially paired with smart trousers and shoes, while colour-blocking with complimentary garments can make for a striking effect. You can put a tee under an open shirt for a relaxed formality, or tuck it under a jumper for a bit of extra warmth.

There are plenty of joys to be found in the t-shirt, but that’s only if you can get one to fit right, which can be harder than it sounds. That’s where we come in, so check out this handy guide to the perfect fit.

What’s your size?

A perfect fit will mean different things to different people, but you’re generally going to want a shape of tee which is flattering to your body shape. Sizes change depending on the brand — you might be a medium in one shop and a large in the next.

How to know if a t-shirt fits

Tightness

A tee shouldn’t be too loose, or it’ll hang awkwardly and make you look shapeless. Too tight and it’ll show your least flattering contours — even if you have a perfectly toned torso, you might look a bit showy in a tight tee. If you’re slim, choose a black t-shirt with a tailored torso so you’re not swallowed up. If you’re larger, choose a structure which gives you some extra room.

Length

If you lift up your arms, the hem of the tee shouldn’t ride up to expose your belly. As a general guide, it should hang lower than your hips, an inch or two below your belt-line, but not all the way to your legs. That said, in certain circles, like skaters, oversized tees are all the rage.

Arms

Shoulder fit is the easiest way to tell if a t-shirt fits you right. The seam along the shoulders should extend across the centre of your shoulder to the very top of your arm. If that’s right, everything else should fall into place. Meanwhile sleeves should go halfway down your upper arm, though some men’s tees have stitched sleeves for a ‘muscle fit’, which is flattering to the definition of your biceps.

Choosing a women's t-shirt according to style