Necklace length is a personal preference, so some of the styles we offer come in several sizes to let you choose.
We recommend experimenting with a length of string, wrapped around like a necklace. This lets you adjust it until you get the length you like, and you can lay it flat against a ruler to measure it.
Another option is to measure the length of a necklace (that you already own) that fits you well. Hold it in the air by one end. This makes sure that the chain is smoothly laid out. Then hold a ruler up to it (vertically), so you are measuring it in the air, from tip to tip.
Here is an example of a 17.7 inch necklace: