There’s a simple rule that covers almost every suit jacket and blazer you’ll ever wear: “sometimes, always, never.”
On a three-button jacket: the top button is buttoned sometimes (optional, mostly a style choice), the middle button is always buttoned when standing, and the bottom button is never buttoned.
On a two-button jacket, the most common style today: the top button is always buttoned when standing, and the bottom button is never buttoned.
On a single-button jacket, typically found on more formal or tuxedo-style jackets: that one button is buttoned when standing.
The reason for the “never” on the bottom button goes back to how jackets are cut. The pattern is drafted so the jacket sits and drapes correctly with the bottom button left open. Buttoning it pulls the fabric in a way that creates visible strain lines across the front and stops the jacket hanging correctly, no matter how well it was tailored.
The other consistent rule: undo all buttons before sitting down. This isn’t just comfort. A buttoned jacket under seated strain is one of the more common ways a jacket’s front seams get pulled or damaged over time.
Waistcoats follow a similar logic to three-button jackets: the bottom button is left undone, again for the same reason: the pattern is drafted to sit correctly with it open. It’s one of those small etiquette details that’s really just following how the garment was engineered to move.
