The phrase "necklace length" refers to the measurement or size of a necklace. It indicates how long the necklace chain or strand is, usually in inches or centimeters, to determine where it sits on the neck when worn. Full definition
The first step is it to learn where different necklace lengths fall on the body for either men or women. (onecklace.com)
She could easily fit her fist into the extra necklace length. (amberforbabies.com)
I also love experimenting with necklace lengths; adding a longer chain underneath a shorter, bigger pieces add dimension and make for some unexpected pizzazz. (cominguprosestheblog.com)