The easiest formula for matching dining chair seat height to your table is simple: table height minus 10 to 12 inches equals the ideal chair seat height. For a 30-inch dining table, a chair seat around 18 to 20 inches usually works well. Always measure from the floor to the underside of the tabletop, not just the top surface, because thick tops or table aprons can reduce knee space. Cushioned chairs may also compress when you sit. The right height keeps your knees, feet, arms, and posture comfortable during meals.