The Short Answer
Kitchen countertops are typically 25-25.5 inches deep (on 24-inch base cabinets), including a 1-inch overhang beyond the cabinet face frame. Bathroom vanity countertops are typically 21-22 inches deep (on 21-inch base cabinets). Island countertops are typically 25 inches deep on the work side, with an overhang of 9-15 inches on the seating side for knee clearance. Custom depths are specified on perimeter countertops with different depth cabinets.