There is often a bit of confusion surrounding these coats and I hope to lend brief insight here to help you make informed distinctions as you continue to build and refine your personal style.
(Please note that I use “coat” and “jacket” interchangeably—they refer to the same article of clothing. However, when I refer to a suit, the “pants” are referred to as trousers, and separate “pants” are referred to as slacks.)
What is a suit jacket?
A suit jacket is precisely that; the jacket belonging to a two (or three) piece outfit including matching trousers and/or vest, which together make a complete suit. The suit jacket always originates from the exact fabric for both (or all) pieces. In other words, being made as part of the whole (ensemble) is an essential feature of a suit jacket.
A suit coat is more formal overall. This is the reason why a suit is the appropriate default for business meetings, weddings (depending on invitation), funerals and other daytime events where sincerity and dignity is expected. The formality of the suit jacket lies in its relative absence of pattern and overt texture, and by being slightly more structured than a sport coat or blazer.
The majority of suits are made of smooth worsted wool in solid conservative colors such as navy and dark shades of grey, and only a few traditional patterns are considered formal enough for a business suit; glen plaid, chalk stripe, windowpane, and pinstripe. However, in today’s modern world, you will also see subtle herringbone, mini houndstooth, tic weave, and birds-eye patterns that play a strong role in the formal suit.
When I refer to structure, I mean that the suit coat has a crisper shoulder and a slightly enhanced canvas. If you’ve seen the Kingsman movie(s), the tailoring of the suits displays a strong structure.
What is a sport coat?
A sport coat is also known as an “odd jacket” – not in the sense of weird, though some sport coat patterns can be quite strange – but rather meaning “different from the slacks”. You might even say that the sport coat is the opposite of the suit coat; more often made with textured fabrics and interesting weaves in a variety of patterns, making it very clear that you are not wearing a suit coat and simultaneously emphasizing the casual-ness of the coat.
The sport coat is something to be worn on informal occasions such as weekends, parties, etc. However, the sport coat is hardly considered casual today compared to the T-shirt, denim or khakis that some other guys are wearing, but is still more casual than the suit.
What is a blazer?
The blazer lives somewhere between the suit and sport coat. While it is a single piece worn with contrasting slacks, traditional blazers are more formal than a sport coat and can resemble some of the more formal structural components of a suit jacket.
Interestingly enough, the blazer is the garment here with the richest history and traditionally needed to fulfill a list of criteria to be defined as such. For example, contrasting gold or silver metal buttons, a crest indicating the wearer is part of an organization, prominent family, or educational institution, almost exclusively solid navy in color, and usually associated with a nautical life.
In today’s modern world, the lines can become blurred a bit when it comes to a blazer as you can find some less structured, buttons which are not metal, and so on. Don’t get caught up in all the traditional blazer details -- simply rely on your clothing professional to present your best looks and options.
What’s the bottom line?
Suit pieces are to be worn together, without exception. Sport coats are colorful and patterned while blazers are solid in a variety of colors – making both of them equally fun to pair with your favorite slacks or denim for a more sophisticated, complete casual look.