That really depends on the build of the wearer. I am about 5’5” tall, athletic build about 135 pounds, and I much prefer the 16-inch standard chain length for all my pearl pendants. It fits perfectly around the base of the neck, and any pendant will come to rest about 1-inch below the hollow in my throat. What I love about the 16-inch chain length is that it won’t catch on my chin when I bend forward (this can lead to breakage if you don’t catch it in time, too!).
The 18-inch chain works well for women over 5’7” and 150 pounds – slightly larger to larger frames; this chain length will rest just slightly lower than the 16-inch will on a smaller frame, and is really nice and versatile. Women with very large frames (over 210lbs) can request a 20-inch chain specially made for them.
The two most popular chain lengths are the 16 and 18-inch.