I was hesitant to purchase this costume since infant sizes are so difficult to determine and the ranges on this particular costume were 0-6 and 6-12. I was in love with this costume though and finally purchased the 6-12 month. It fit perfectly! My daughter was 6months and 3 weeks, just shy of 16 pounds and 27.5 inches long. There was maybe 3 inches to spare in the feet but the body fit great. The hat was a perfect fit and her head is 17inches in circumference. Just thought I'd add some measurements so it helps the next person. It was also a nice weight, not too warm but just enough. It was soft and my daughter didn't mind having it or the hat on. The carrot rattle was a great little addition too!