Take a walk through any downtown business district today and you’ll see the modern man's business uniform: a pair of dark suit trousers, a button-up shirt, a shiny tie, and a pair of dull, duck-billed shoes. Many men have given up on suit jackets, and for good reason. Most of them look like Willy Loman in one. Some, however, look tremendous with their jacket on; the difference is in how their jacket fits.

So how should a suit jacket or sport coat fit?

The outline of the jacket should flow smoothly and cleanly. There shouldn't be any puckering due to the jacket being too tight, or drooping due to it being too big. You should look and feel comfortable.

More specifically, you can check for the following details:

• Collar: Perhaps most fundamental is the collar, which should always stay glued to your neck, even as you move around.

• Shoulders: Whether padded or soft, your jacket’s shoulders should always lay smoothly across your own natural shoulders, and terminate close to your shoulder joints.

• Fastening point: The fastening point is the center button on a three-button jacket, and the top button on a two-button jacket. This should be around your natural waist, which is located just above your navel. If the fastening-point is too high, your jacket can make you look beer-bellied when buttoned.

• Mid-section: When your coat is fastened, you should make sure there’s not a big “X” across your stomach, making you look like some Marvel comic book character. If there is, the jacket is too tight and needs to be let out.

• Length: Jacket length is a matter of taste, but generally speaking, the jacket’s hem should be equidistant from your collar and the floor.

• Armholes: Your armholes should be high enough to allow you to (reasonably) move your arms around without disturbing your jacket. Pay particular attention to whether your jacket’s collar lifts off your neck.

• Vents: Vents are typically sewn shut when a jacket is new, but once this thread is removed, they should remain closed and not flare out or gape. 

Of course, fashion brands may have their own interpretations of fit, but the above stands as a general guideline for how any man can look good in a tailored jacket. As Bruce Boyer once wrote, “anyone can look ridiculous; some men choose not to.”