Is the passenger capacity of the A350 really only 250 pax? I read online that the capacity of an A350 was 250 passengers, but I took the max cabin width and length of an A350-900XWB, and I ended up with a 400 passenger capacity in a 4-class layout.


Economy was a 3-3-3 configuration, with 2.48 feet seat pitch
Premium was a 2-4-2 config. with a 3 feet seat pitch
Business was a 2-2-2 config. with a full 6 feet seat pitch
First class had a wide 1-2-1 configuration with a full lie flat bed to make for a 7 feet seat pitch


Yet, I still got a capacity way higher than 250 of 234 economy seats, 54 premium seats, 42 buisness seats, and 16 first class seats, and the total for 346 passengers + 8 crew! Yes, I included washrooms for all classes, emergency exits, and the galleys. What does the capacity of 250 really mean?
Airbus themselves give max passenger seating 440, and typical seating 3-class 300-350, for the A350-900. https://www.airbus.com/aircraft/passenger-aircraft/a350xwb-family/a350-900.html

The undeveloped A350-800 is listed with 276 passengers. Maybe that's where you got your 250 number.