The 787-8 is designed to seat 234 passengers in a three-class setup, 240 in two-class domestic configuration, and 296 passengers in a high-density economy arrangement. Seat rows can be arranged in four to six abreast in first or business (e.g., 1𣇻, 2𣇼), with eight or nine abreast in economy (e.g., 3𣇽, 2𣯔, 3𣛩). Typical seat room ranges from 46 to 61 in (120 to 150 cm) pitch in first, 36 to 39 in (91 to 99 cm) in business, and 32 to 34 in (81 to 86 cm) in economy.

Cabin interior width is approximately 18 feet (550 cm) at armrest,[190] 1 inch (2.5 cm) more than originally planned, and 15 inches (38 cm) more than that of the Airbus A330 and A340, while 5 inches (13 cm) less than the A350 and 16 in (41 cm) less than the 777.[194] Airlines use economy seat widths that range from 16.33 in (41.5 cm) to 20.66 in (52.5 cm), although published seat research studies recommend a minimum 18-inch (46 cm) seat width. 787 economy seats are approximately 17.2 inches (44 cm) for nine-abreast seating, and 19 inches (48 cm) wide for eight-abreast seating arrangements. Most airlines are selecting the nine-abreast (3𣛩) configuration.