Not sure about the length of necklace you need? Let this chart help you with that. Depending on the outfit, sometimes it is hard to know exactly.
14" Collar length- v-necks, open collared shirts, boatnecks
16" Choker length- goes with most outfits
18" Princess length- almost all outfits
20" Matinee length- collared shirts, high necklines, business outfits
24" Opera length- turtlenecks, boatnecks, collared shirts
30+" Rope length- evening wear or business outfits. Can be doubled easily