When looking for a pearl necklace, there are a few things to consider.
First, the type of pearls you want. There are four types of pearls: Akoya, Freshwater, South Sea and Tahitian.
Akoya are cultured saltwater pearls. They are usually white with rose undertones. They range from 6-8mm in diameter with 8mm being the large size.
Freshwater pearls are cultured pearls that are not as symmetrical as Akoya pearls. They are also white with fewer lusters. The average size ranges from 5-6.5mm in diameter.
South Sea pearls are cultured pearls that are usually white with silver or rose undertones. They are one of the larger pearls with sizes ranging from 11-13mm in diameter.
Tahitian pearls are cultured pearls that are usually black with green or pink undertones. They are also large with sizes ranging from 11-12mm in diameter.

Once you have the type of pearls, the size of the pearls will follow. From smallest to largest, the pearl sizes are freshwater, Akoya, Tahitian and South Sea. Depending on personal preference, every pearl has its advantages.
Next, you must pick out the type of pearl necklace you want. There are several popular lengths.
Choker is a pearl necklace that is 14-16 inches in length. It is close to the neck and looks beautiful for formal or business wear.
Princess is a pearl necklace that's 17 to 20 inches in length. You can wear this length anywhere, from work, play or with formal attire.
Matinee is a pearl necklace that is 20-24 inches in length. It is a little bit longer and is great for business wear.
Opera is a pearl necklace that is 28 to 34 inches in length. It is perfect for formal evenings.
Rope is a pearl necklace that is 45 inches +. You can wear this in the evening or for formals events.
Once you figure out the type, color, size and length of your pearl necklace, be sure to take care of it so it can last for years.
Keep your pearl necklace away from household cleaners or beauty products. Wipe your pearls with a soft cloth and wear your pearl necklace to keep it lustrous. Pearl necklaces with strong nacre will last longer. With these tips, your pearl necklace should last you for years.