If you have a single button suit or jacket, you should wear it fastened when standing or walking and leave it open when sitting so you don't pull the fabric. A bonus of wearing your jacket unbuttoned when sitting is that you'll be more comfortable and look like a gentleman who knows his style.
Buttoning Rules For Single-Breasted Suit Jackets:
These jackets should ALWAYS be buttoned when standing. Unbutton the jacket when sitting down, so that it doesn't crease. The traditional way to button a two-button jacket is to Always fasten the top button and leave the lower undone.
As a general rule of formal wear etiquette, a jacket should be buttoned when standing and unbuttoned when seated. Of course, there are additional rules too. On a two-button jacket, only use the top one when it's time to button up.
With a single-breasted, three-button suit, simply close the middle button, always. The top button is optional and can be buttoned up or left undone. The bottom button, again, should never be buttoned, as it will put a strain on the fabric of the suit jacket and will not look flattering.
As you probably guessed, this rule is primarily for 3 button jackets. You can start by fastening the top button “Sometimes” as a personal preference when the middle button is also fastened. The second or middle button should “Always” be fastened, and the last or bottom button should always remain open.
When wearing a suit, always leave the bottom button open for the waistcoat and jacket. The tradition dates back to King Edward VII from the early 1900s. He unbuttoned the bottom of his waistcoat because he was too fat. He unbuttoned the bottom of his jacket to pay homage to the riding jacket that suits replaced.
The top button is all you need. The two-button jacket should never be buttoned completely. The three-button suit, like others, comes with a simple rule: "sometimes, always, never." This means you should sometimes fasten the top button (if you want to), always fasten the middle button, and never fasten the bottom.
We always remember one simple suit etiquette rule when wearing a blazer: “sometimes, always, never”. If you have a three-buttoned jacket, 'sometimes' button the top one, 'always' button the middle, and 'never' button the bottom. With a two-buttoned suit, 'always' button the top button and 'never' the second.
The top button is all you need. The two-button jacket should never have both buttons fastened. The three-button suit comes with a simple rule: "sometimes, always, never." It means you should sometimes fasten the top button (if you feel like it), always fasten the middle button, and never button the third.
The shoulders of a suit jacket should feel comfortably snug, with the end of the shoulder seam meeting the tip of your own shoulders. The shoulder should sit flat, without any rumpling, with the top of the sleeve hanging beautifully straight from the shoulder point, with no wrinkling at the top.
The button should close without strain, and there should be no wrinkles radiating out from the closure. A little bit of an opening at the bottom of the suit is fine, but the two halves beneath the button shouldn't pull apart so far that you can see a large triangle of shirt above your trousers.
– Always leave the bottom button undone on a single breasted waistcoat. This is optional on a double breasted. – A slim cut is essential – you don't want it to billow.
However, as the tradition has been to leave the last button undone for such a long time, suits and waistcoats are actually designed for this purpose. Whether it's a sports jacket, blazer, suit jacket or waistcoat, they're now cut in such a way as to drape (and look) best when the bottom button is undone.
How to wear a 3 piece suit? Jacket can be worn buttoned or unbuttoned. The waistcoat must always be worn buttoned all the way up, leaving the bottom button open. In the past the open bottom button prevented the waistcoat from riding-up when on horseback.
Only the top button of the suit coat is buttoned. The bottom button is never buttoned. Unbutton your jacket when you sit down. Make sure about a quarter inch of shirt cuff is showing.
You Don't Cut The Vent Threads
A vent is a slit up the back of your jacket. Like all manner of menswear details, they're leftover from the suit's time as uniform – it let the jacket sit over a saddle without bunching. Italianate tailoring tends to be single-vented, whereas British suits prefer a slit up each side.
You should be able to move your opposite palms(arms crossed) to the top of your shoulder freely with the top or middle button closed, at least in an off the rack suit.
Suit Button Rules: Double-Breasted Suit Jackets
Simply button every button with working buttonholes. The bottom right button, however, is optional. Even when sitting, all buttons (except the optional bottom) should be buttoned on double-breasted jackets.
Buttoning rules for two-button suit jackets
The traditional way to button a two-button jacket is to fasten the top button and leave the lower undone. The top button on these jackets should ALWAYS be buttoned when standing. Unbutton the jacket only when sitting down to avoid creases.
Your suit jacket should cover about 80% of your butt and crotch. Generally, the bottom edge of a jacket should end between the two knuckles on your thumb. This rule can be pushed a little bit when wearing a casual sport coat because they tend to be a little shorter.
If you can easily fit a fist between the buttoned jacket and your stomach, it's too loose. The jacket length – with your arms straight down at your sides, your jacket should be at the same level as your knuckles.