After all, she is not going to be wearing military dog tags. A necklace is a nice piece of jewelry. Common lengths for necklaces are: Collar -- 12 to 13 inches; Choker 14 to 16 inches; Princess 17 to 19 inches; Matinee 20 to 24 inches; Opera 28 to 34 inches; and Rope or Lariat over 45 inches.