When the groom tries on his tux or suit, he should try sitting with the jacket buttoned to make sure it still fits comfortably. The groom's shirt should also fit comfortably around his neck, shoulders and waist. If he chooses to wear a vest, it should fall just over the trousers waistband. Vests usually have a slide strap to adjust it to their waistline. It should fit comfortably across the chest and the buttons should line up to the front of his jacket.
Many trousers have waistbands that are adjustable.
The hem of the trousers should come just over his shoe tops.