The old Y class was a 17.5 inch seat, i don't know the width of the new seats, but probably a little wider, since some FA report that the aisles seem smaller.

17.5"x 4 plus 3 x 1 inch installation clearance = approx 3 inches or roughly 187 cm.


Source

http://www.cheapflights.co.uk/misc/legroom_report.html