Should you be able to button up a blazer?
Regardless, no matter what kind of suit you're wearing, the bottom button should never be buttoned up. For a waistcoat, there's a similar rule: always leave the bottom button open.
Your blazer should be fitted (not tight!) across your shoulders. The hem of your blazer should skim your hipbone. The sleeves of your blazer should hit mid-thumb when your arms are down at your sides.
The industry standard is that each side of you blazer must be able to go across half of a breast. Buttoning should not cause your blazer to appear (or feel) tight and create a too tight look.
Nowadays the fashion is for suit jackets and blazers to have two-buttons. 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.
"If you're wearing a suit or blazer to a wedding or formal event, you should never leave your jacket open—but if you're wearing a blazer casually with chinos or jeans, you can keep it relaxed and open."
The sleeve of your suit jacket should rest just above the hinge where your hand meets your wrist. If all of your jackets are tailored to this point and your shirts fit properly, you'll always show the proper amount of shirt cuff, which should be between 1/4" - 1/2".
When closing the jacket, the middle button should always be closed, and the top two or all three is also considered correct etiquette for women. For short-bodied ladies, the jacket usually fits better and flatters the figure when the lowest button is left unbuttoned.
Depending on the torso length, the blazer should end around two or three finger widths from the crotch-line. This length can have a large variety of button styles, pockets and lapels.
When buttoned, the lapels of your blazer should only be loose enough to fit a tightened fist between the fabric and your chest, and they should be snug to your chest.
Women's Blazers & Suit Jackets: To Button or Not To Button? The rule is so simple for men: When they stand up, the top button of their suit jacket should be buttoned; when they sit down, they can unbutton.
Should sport coat be buttoned?
You don't have to button it or unbutton it any time, but it usually looks better and helps to slim your silhouette to have it buttoned when you're standing. Button the top button only, if there are multiple buttons on the jacket.
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.
Women's Blazers & Suit Jackets: To Button or Not To Button? The rule is so simple for men: When they stand up, the top button of their suit jacket should be buttoned; when they sit down, they can unbutton. For women: Meh. Not so simple (Surprise!).
Measured to not hang over your hands or rise up your arms, the sleeves should land somewhere between your wrist and your thumb. When buttoned, the lapels of your blazer should only be loose enough to fit a tightened fist between the fabric and your chest, and they should be snug to your chest.
