Airbus A350 vs Boeing 787: the A350 wins economy by about an inch
The A350 and 787 look interchangeable on a booking page. In economy they are not: A350 seats run a median 18 inches wide against 17.1 on the 787. Where that inch comes from, and the one airline that erases it.
- A350 economy seats: median 18 inches wide. The 787 equivalent: 17.1.
- Both fly nine-abreast, so the gap is fuselage, not layout.
- Japan Airlines' eight-abreast 787 beats every A350 here at 18.5 inches.
- In business class the airframe tells you nothing. Width ranges 18.7 to 35 inches.
The short answer
In economy, the Airbus A350 is the wider seat. Across A350 configurations on SeatInside that publish dimensions, the median economy seat is 18 inches wide against 17.1 inches on the Boeing 787, and 31 of 33 A350 configurations reach 18 inches or more. Both aircraft normally fly nine-abreast, so the gap comes from the A350's wider fuselage rather than a different layout. The exception is Japan Airlines, which seats its 787s eight-abreast at 18 to 18.5 inches — wider than any A350 in the set. In business class the aircraft type is not predictive: seat width there ranges from 18.7 to 35 inches depending on which product the airline bought.
The inch is real, and it is the whole argument
Thirty-three A350 configurations on SeatInside publish economy seat dimensions. Thirty-one of them seat 18 inches or wider. Run the same query against the 787 and you get 48 configurations with a median of 17.1 inches, of which five reach 18.
Nine-tenths of an inch sounds like nothing until you multiply it across a nine-abreast row, where it adds up to most of a seat's worth of cabin width. That is exactly what it buys: the A350 holds a 3-3-3 economy layout at 18 inches, and the 787 holds the same 3-3-3 at 17.1.
Airbus built the A350 fuselage wider than the 787's. Both manufacturers market nine-abreast as the standard economy arrangement, and nearly every airline took the standard on both aircraft. So the fuselage difference does not get absorbed by a different layout. It lands in your shoulders.
Japan Airlines is the exception, and it is not close
Five 787 configurations here seat 18 inches or wider. All five belong to Japan Airlines, which lays out its 787-8 and 787-9 cabins eight-abreast in a 2-4-2 arrangement at 18 to 18.5 inches — wider than any A350 in the set.
The cost of that decision shows up in the seat count. A JAL 787-9 carries 195 passengers. An ANA 787-9 carries 395. Same airframe, same home market, and one airline is flying twice the people.
So the useful rule is narrower than "A350 beats 787." If the 787 is a JAL 787, take it over almost any A350.
Business class: the airframe tells you nothing
Business-class seat width across the configurations on SeatInside runs from 18.7 inches to 35, median 21. Pitch runs from 32 inches to 82. Nothing in that spread tracks the aircraft type, because it is a record of which seat the airline ordered.
An A350 fitted with an older angled recliner loses to a 787 with a modern reverse-herringbone suite, and the reverse is just as true. The airframe question is settled in economy and meaningless up front.
What to actually do with this
For a nine-abreast economy cabin, the A350 is the better default, and now you know the size of the bet: roughly an inch of shoulder room.
Then stop comparing types and open the specific configuration, because the spread inside one type dwarfs the gap between the two. A350-900 cabins here run from 161 seats to 411 — a 2.5x range on one aircraft.