Originally Posted by triplefives

Agree with percysmith's math, but want to add that some airlines play with their seat width and armrest measurements so they are not always a like for like comparison.

For example, SQ, on seatguru, lists the seat measurement at 19 inches for their 777WR/N product (the new one), but, from flying with them, I can tell you the armrest is slimmer in order to make the 19 inch number. Armrest might have been 1.5 or 1.75 inches. I didn't get a tape measure to confirm but I've put in a lot of butt in seat miles across different carriers so the difference was definitely noticeable.