We’ve deciphered the world’s toughest dress code so you don’t have to.

What is smart casual? Why is it so difficult to get it right? And how do you nail it? When former US President Barack Obama was in office, he told Vanity Fair magazine, “I wear only grey or blue suits. I’m trying to pare down decisions… because I have too many other decisions to make.” Smart casual represents the exact opposite of this approach. If the invitation asks you to dress “smart casual”, every single item you put on requires consideration in its own right, and in relation to every other item you’re thinking of wearing. White tennis shoes could be right, but so could brown leather Oxfords. On the upper body a plain cotton T-shirt may work, but so might a white shirt and a silk tie. Given this range of possibilities, it’s not easy to feel like you’ve conquered it, but that’s why MR PORTER is here. We’ve obsessed over the combinations, ached over the details, and argued about whether or not it ever calls for a tie. All so that you don’t have to.

But before we get to the nuts and bolts, let’s remind ourselves about the purpose of the smart-casual dress code. When the term was first introduced in the 1990s, the “casual” part announced the direction of travel, while the word “smart” applied some brakes. In 1996 in the UK, an influential book called Debrett’s New Guide To Etiquette & Modern Manners thought that smart casual, “…has to look presentable, but not too formal.” The book suggested that, “The pivotal garment for men is a blazer or other sports jacket.” Bear in mind that, until then, it had been far more common for guys to wear suits to events; 23 years later the world is different, and for many men a smart-casual dress code is now an exhortation to dress up, rather than an invitation to dress down. This means that the big question is, how formal do you go?

First, let’s eliminate some options. It’s not a request to dress casually, otherwise there would be no dress code, or it would just say casual. Nor is it a formal dress code, because it doesn’t ask for dinner jackets, lounge suits or even jackets and ties. The problem is that there’s a lot of space between these opposite ends of the spectrum, but little agreement about what constitutes smart and what constitutes casual. Some men think anything tidier than board shorts and flip-flops looks smart, while others don’t feel comfortable leaving the house unless they’re in a jacket and tie. All of this makes it very tempting to contemplate the meaning of status in contemporary society, the prioritisation of physical comfort, and the rights and wrongs of self-expression, none of which will help you when you’re staring into your closet wondering what the hell to wear.

For this reason we’ll break down the elements that make up a smart-casual outfit, and consider how best to put them back together. It’s helpful from the outset to think about how the garments combine. Is the overall effect leaning too hard towards casual, or too hard towards smart? If you take the most formal option in every category, then you’ll look very smart. While if you take the most relaxed option in every category, you’ll end up looking very casual. Both of these outcomes could be the right one depending on the event in question, it’s just a question of being aware of the overall impression made by your outfit.

Finally, even within the latitude afforded by smart casual, there are a few rules:

Unless you’re in the entertainment industry, business events call for smarter and more conservative combinations than social events (don’t wear denim, and hold back on individual flourishes such as jewellery or pocket squares).

What works best during the day differs from what works best at night. Sand-coloured chinos, and other earthy colours, work best during daylight hours, while velvet should be saved for evening events.

If you’re in any doubt, then you should put on a blazer or tailored jacket; you can always take it off if you feel overdressed when you arrive.

Next, the specifics.

A man’s timepiece might not be the most obvious place to start to build an outfit, but it’s actually a powerful statement of intent. Like it or not, your watch speaks volumes about your lifestyle, your taste, and, inevitably, your income bracket. To take two extreme examples, an Officine Panerai Submersible advertises its wearer as a man of action (given its 47mm diameter, all that action has hopefully built up a pair of muscular forearms), while a gold Cartier Tank Américaine strongly hints that its wearer is refined and cultured. And despite the fact that a man can be both of these things, we still advise that he should only wear one watch at a time.

The more formal the outfit, the more elegant the watch should be. So if you’re in a white shirt and a blazer, something refined such as a Jaeger-LeCoultre Reverso is ideal.

A bigger, sportier watch works best without a jacket. If you’re still saving for that Holy Grail watch, a vintage Swatch is another stylish choice for formal outfits, makes your net worth hard to pin down, and sends out a message of self-confidence in a status-obsessed world.

Smart casual could involve many different shoe styles, including espadrilles and sneakers, but if you’re not wearing proper, Goodyear-welted, leather-soled shoes, you need to know why. The decision needs to be made in the round, so espadrilles might work, but probably only if you’re dressing down in a pale-coloured summer suit; combine them with casual trousers and the effect will be too relaxed.

If you are wearing more casual trousers, dress them up with a pair of traditional, hard-soled Chelsea boots, or try a pair of loafers in dark-brown leather, or tobacco-coloured suede. In the evening, switch out suede loafers for leather ones (suede looks dull under artificial light). Driving shoes are not a substitute for classic loafers, but could work if the rest of the outfit is very smart – an elegant pair would complement a rumpled flannel suit and a rollneck sweater in the evening. Alternatively, suede desert boots walk a fine line between smart and casual and look particularly good with cotton suits to convey an image that’s both dressed up and relaxed.

For an edgier look, try simple white sneakers (such as Common Projects or Converse) with a casual suit, particularly for events such as gallery openings or casual weddings. One thing: just make sure they are box-fresh, rather than battered almost to destruction. You don’t want to look like a rebellious teen.

As with leather shoes, there are circumstances in which a shirt is unnecessary, but wearing one is definitely the default option. Work on the basis that all corporate events call for a shirt, and that you can only ever wear a T-shirt under a tailored jacket. However, the smooth, very slightly shiny dress shirts that are normally worn with a suit are not always the best option in a smart-casual outfit.

If you’re looking for a plain colour, how about a white or pale-blue Oxford-cotton button-down? You could mix a white Oxford shirt, a blue blazer, a pair of jeans and some leather loafers for a classic look.

If the event is more on the arty side, you could wear a fashion-oriented shirt with a plain pair of loose-fitting dark wool trousers. You have the bones of smartness with added style points thrown in here.

If the mood is very relaxed (think beach wedding), then consider a linen shirt (maybe with a Nehru collar) or a half-placket, or popover shirt, and combine this with a loose-fitting pair of cotton trousers.

In the evening, white shirts are always a good choice, whether in the form of a crisp poplin shirt for smarter events, or a more casual linen version when the weather warms up.

British musician Mr Phil Collins named his 1985 album No Jacket Required, after an incident in which he and Led Zeppelin’s Mr Robert Plant were turned away by a restaurant in Chicago because Mr Collins wasn’t wearing a “proper” jacket. However, unless you’re a world-famous rock singer, it may be that in actual fact a jacket is required. If you go for this option, it’s important that the jacket doesn’t look like the top half of a suit, and this is down to the details.

Look for blazers with some or all of the following: patch pockets, brown or brass buttons, or textured fabrics, including linen, or linen and silk mixes. These give added depth and generally make the wearer look better.

Another strategy is to go for a cotton jacket, which will immediately seem different from business attire; look for a casual cotton blazer that’s reminiscent of a bleu de travail, the hip French workwear jacket.

Of course, other colours of jacket are also appropriate; pale colours, plain or patterned, work well for daytime events (khaki is popular this season), while velvet is a great option for non-corporate evening events.

Just 20 years ago, smart-casual trousers were synonymous with beige cotton chinos. The good news is that now the options are rather more varied, while the bad news is that now the options are rather more varied.

A man who reaches for a pair of biscuit-coloured chinos won’t be wrong to do so; try a pair with a white shirt, a blue blazer and pair of suede desert boots for a warm-weather outfit.

However, if you don’t want or need to wear a jacket, then consider a darker pair of chinos, perhaps in a shade of blue or green, worn with Chelsea boots and a white shirt for a daytime look.

It’s worth noting that chinos are always a bit smarter than five-pocket canvas jeans. Strike a different tone by going for a pair of blue jeans (avoiding embellishments and distressing), but dressing up in other departments with leather loafers, a shirt and a blazer. We’d even be tempted to add a striped silk tie to this outfit for a classic American look.

Alternatively, go for a pair of fine corduroy trousers (all the rage this season), a matching corduroy jacket, a plain cotton tee and a pair of simple sneakers.

Nighttime events could make good use of a pair of dark wool trousers and a white shirt. Although it’s worth bearing in mind that you’ll need clothes cut sufficiently fashionably (loose-fitting trousers and an embellished shirt, for example) so that you’re not mistaken for a member of the waiting staff.

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