I've seen a lot of bad advice on Reddit regarding suit jackets being worn as blazers. I've seen a lot of that advice getting upvoted. In particular, there was one thread where people were telling a guy to throw out his old suit jacket after he lost his pants. That is terrible advice. I've also seen some of this bad advice upvoted in SQ. So I want to clarify some things -- at least from my perspective.

What is the difference between a suit jacket and a blazer?

Some of you don't seem to understand this. While certain details are more appropriate for blazers than suit jackets, those aren't the defining distinction. The difference between a suit jacket and blazer is the existence of matching pants. If there are no matching pants, it's a blazer. If there are, it's a suit jacket. That's it. (The difference between a blazer and a sportcoat is technically pattern -- a blazer has to be solid -- but nobody knows or cares about that).

Generally, a Blazer might be a more casual thing. Certain fabrics like hopsack, tweed, and wool flannel might be better for a blazer than for a suit. High-contrast buttons like gold buttons are really not right for a suit but at home on a blazer. Patch pockets and minimal structure look more casual, too, so they might be better on a blazer. But these details are not part of the definition, so, when you're wearing a suit jacket without the matching pants, you are, as far as anybody else knows, wearing a blazer.

Here's a suit with patch pockets. Here's Jason Jules in another suit with patch pockets. Here are a bunch of blazers with various types of pockets and buttons (although The Rake uses a more historical / naval definition).

This is crucial, and so many people are getting it wrong. The objects are the same. The difference is metaphysical -- it's the existence of matching pants.

Be prepared to forsake the suit.

If you can style it right, the main reason not to wear a suit jacket as a blazer has to do with wear and tear.

If you wear and dry clean your suit jacket and pants together, they will wear at the same rate and retain the same color. They'll look better together.

But if you wear hem apart from one another, they will wear differently, and you might not be able to wear them together anymore.

If you're willing to accept that risk, you're too poor to buy a separate blazer, or you lost your pants, then congratulations: your suit jacket is now a blazer. It's that easy!

But you still need to worry about styling! So let's consider the normal styling concerns for blazers, all of which apply for wearing suit jackets as blazers, since they're the same damn things.

Make sure the colors work.

Since a suit is a matching combination, a blazer and the trousers you wear with it have to not match. How not-matchy is not-matchy enough?

This can be hard to put into words. I could tell you that you can or can't wear navy with charcoal, or medium blue, but the reality is that... It depends. Here is a navy blazer with charcoal pants, and they look great together. Here's another.

It depends on the shades of those colors, the lighting of the room you're going to be in, and how well people think you normally dress -- they'll be quicker to judge you if they think you're likely to mess this up.

At the end of the day, the only hard rule is, the colors need to contrast enough, given the context, that people can tell that you are dressing with intentionality. If that's too vague a rule for you, welcome to the sub.

As a final note, remember that black is weird in the US, and hard to pair with anywhere.

Make sure the patterns work together.

When it came to color, we require clear contrast. In pattern, however, we have some choices. These relate pretty reasonably to your usual pattern concerns -- the main thing being, don't clash.

Solid + solid is a perfectly good combination. Solid + pattern usually works as well. Matching patterns (other than solid) is probably bad. Any two loud patterns are probably bad. A loud pattern and a subdued pattern might work -- when in doubt, look for a second opinion.

Note that a contrasting pattern might help a lot in a relatively low-contrast color pairing. For example, while navy + dark charcoal is a difficult combination, solid navy + heavily specked dark charcoal might look great.

Make sure the fabrics work together.

As with pattern, the rules here are not very simple. But there is a good guiding principle. Generally, two fabrics have to match, or at least not clash, in formality and seasonality.

The clearest example here would be wearing linen with tweed or wool flannel. You'll probably be uncomfortable in that combination anyway, wherever you go... But you'll also look dumb. (It should also go without saying that tuxedo pants and dinner jackets should only be worn with other eveningwear).

But at the margins, things get hazy. Can you wear a tweed sportcoat with a midweight chino? Can you wear your highly structured navy suit jacket with burgundy chinos with slant pockets but no crease? Can you wear your white double breasted wool-silk-linen blend with lightweight jeans? These are all good, weird questions.

Consider other factors.

These factors don't really have hard and fast rules, but are worth considering.

  • Fit. You might try a slim-fitting blazer with high-rise wide-legged pants, cropped pants, pants with or without socks... Again, do this with intentionality.
  • Shirt -- a solid white dress shirt works with everything... unless you're trying to dress things down. You have to remember not to clash patterns, and keep things in the same season / formality bracket.
  • Shoes -- the shoes have to work with the pants, and match the belt. Then, they have to match overall formality. Wearing bluchers can be a good way to signify that you're not trying to wear a suit (even though a suit + bluchers is not necessarily wrong -- oxfords are preferred, but bluchers can definitely work -- it's a step down, which corresponds better to blazer + odd trousers).
  • Accessories -- you still don't want to over-accessorize. Some accessories, like a tie, up the formality. Others, like a pocket square, allow you to play with another contrasting fabric and add some flair to an otherwise boring look. You can match metals between a watch, blazer buttons, belt, and any shoe hardware to show more intentionality. You can do a lot here.
  • Waistcoat -- don't do something silly like match a waistcoat to one thing but not the other. A matching waistcoat + blazer with odd trousers will probably look awful.