The size 18/ XL in Ralph Lauren is closest to the following:
Brand Label Weight (lbs) Height (inches)
Hatley 12 - 59 inches
J.Crew/ Crewcuts 16 110 - 125 lbs 64 - 68 inches
LLBean 16-18/XL - 64 inches
Marimekko 12 yrs/ 152 cm - 61 inches
MiniBoden 12y - 60 inches
Ralph Lauren 18/ XL 116 - 126 lbs 64 - 66 inches