Finding the right length necklace can be hard. Thankfully, unlike buying jeans sizing across necklaces is the same since we use inches (or centimeters).
What a necklace will look like on you depends on the size of your neck. The best way to identify the right size for you is to take some yarn/string and wrap it around your neck to your preferred length then measure it (apply this to bracelets too).
Below are images of various sized people so you can get an idea of what lengths look like. Note that smaller necks are able to wear our 12-14 inch necklaces as chokers and people with larger necks wear our 16-18 inch necklaces as chokers.