Chains vary not only by the type of links, but also by their length and how they are meant to be worn. Although you'll find exceptions, most necklaces fall into one of the below categories:
Choker or Collar Necklace Length
These are meant to be worn just above the collarbones, around the base of the neck. This length emphasizes the shoulders and is well-suited to shirts with high necklines. Chokers are usually 16 inches in length or shorter.
Princess Necklace Length
Princess length chains are one of the most popular styles, hanging over the collarbones to display a pendant. These chains are typically 18 inches long.
Opera Necklace Length
Also called matinee necklaces, opera length chains are longer and are usually worn over a shirt or blouse with a pendant. Most opera chains are 24 inches in length.
Rope Necklace Length
Rope chains can be 30 inches or longer, draping over clothing to create dramatic style. Ropes are usually worn without a pendant, although a shorter version may be adorned with a large, dangling metal or gemstone design. Ropes can be wider chains or they can be fine and very long, worn looped around the neck several times at different lengths.