There are a variety of necklace lengths in my shop as well as adjustable necklaces.  I wanted to show a chart to demonstrate a better explanation of where necklaces would fall on your body based on both the length of the necklace and how I describe the necklace in words in my shop.  For example, most of my necklaces that are 16 inches or under I describe as chokers, and the very short chokers 14 inches or less I also refer to as collars.  Please see the diagram below:  

Although there are more lengths on the left, you can get the basic idea of what lengths would be called.  Please note that this is only an example and that is for the average sized person.  I am a fairly small person, and for a collar necklace to actualy sit up on my neck like that it would have to be about 12 1/4 inches.  Similarly, the other lengths hang a bit further down on me because my neck is small.  If you would like to have the most accurate idea of where a necklace will fall on your frame, it is best to use a measuring tape.

Also, for the average male frame, an 18 inch necklace would hang approximately where the 16 inch is sitting on the female in the chart.