Pearl Paradise at www.pearlparadise.com offers these descriptions for pearl necklace lengths and what to wear for the 6 typical length necklaces.
In brief, "Choosing Your Pearl Necklace Length" (http://www.pearlparadise.com/pearlnecklace.html):
1. Collar: 12 - 13 inches. They are usually made up of three or more strands. Ideal complement to boat neck, V-neck, or off-the-shoulder fashions.
2. Choker: 14 - 16 inches. This classic is appropriate with everything from casual to formal eveningwear, and complements almost any neckline.
3. Princess: 17 - 19 inches. The most common length for a pearl necklace, well suited for crew and high necklines, but also complements low, plunging necklines.
4. Matinee: 20 - 24 inches. Ideal choice for casual or business attire. Best with high necklines, but also very well suited for long sundresses and formal gowns.
5. Opera: 26 to 36 inches. It can be worn as a single strand with high necklaces or doubled to create a two-strand choker. It can be knotted at the neckline or above the bust. Traditionally, opera length necklaces are worn with eveningwear, although using them to accessorize more casual attire is also appropriate.
6. Rope: 37 inches or longer. It can be made with several clasps, enabling it to be broken down into different necklace and bracelet combinations, or doubled and even tripled to create a multi-strand choker. May also be tied in a knot and worn down the front or slung over the shoulder to accentuate a backless dress.
For more pearl information, see www.pearlparadise.com