Historically, in the early years of the suit as everyday menswear, it appears there were no formal buttoning rules. Look to trade magazines and illustrations from the earlier part of the 20th century, and one sees jackets with between one and five buttons, each buttoned in a manner that suited the personality of the wearer or the cut of the garment. According to the lore of menswear, this all changed in the early 1900s when King Edward VII started the trend of leaving the bottom button of a suit undone. Apparently, he grew so big in his stomach, that he wasn’t able to button the bottom button of his waistcoat and jacket. In order to not offend the king or draw attention to his weight in a negative manner, his employees began to follow the same trend. The custom then gradually spread across the world and everyone began to follow this same process as the new standard.
General Buttoning Rule
The general rule of thumb when buttoning your jacket is that a suit should always remain buttoned (except for the bottom button in a two or more button jacket) when standing. When you sit you unbutton the jacket, as it is usually necessary and then promptly re-button the jacket whenever you stand again.
One Button Suits
One button suits are the easiest to remember as they follow the general buttoning rule to the letter since there are no extra buttons to worry about.
Two Button Suits
With the two-button suit, the top button should always remain buttoned when standing but the bottom button should remain open. Not only does using both buttons restrict movement, but it creates an awkward shape and fall of the suit on most silhouettes.
Three Button Suit
With this suit there are a couple options. You can fasten the top two buttons and leave the bottom one open, or you can simply button the middle button. The most common method is keeping the top two fastened, however some jackets have a soft lapel roll that can extend into the top button. When this is the case, attempting to still fasten the top button will just create an awkward unbalanced look in the jacket and lapel so you want to stick with just the middle button.
4 or 5 Button Suits
These are generally not seen in today’s fashion and even with a long torso seem to have a very dated feel so you won’t usually see them in most closets. However if it is a style that works for you then just remember to stick with the general rule and leave the bottom button undone. The top 3 or 4 should remained fastened.
Double- Breasted Suits
Also a very easy option as normally you would leave all the buttons fastened except for the bottom one until you are ready to sit, at which point you would open all of them. However this rule tends to be optional with the double-breasted suit as you are welcome to keep them all fastened as well. Prince Charles is the best example of using this method consistently. There are many different button arrangements in double-breasted suit but the above rule general applies whether you are wearing a 6 button or 4 button or any other combination. You can button all the functional buttons or just leave the bottom one undone depending on what flatters you figure the most.