Chain Length Math
So your pendant doesn't hang at the right length, how to figure out the correct length? Keep in mind that the chain will travel twice the distance that you need since it's coming down from both sides of your neck. In other words, if your chain is 16 inches long, but you'd like the pendant to hang 2 inches lower that means you'll need a 20 inch chain.
Precious metal chains are usually manufactured in 16, 18, 20, 24 and 30 inch lengths. Anything else will require a jeweler cutting and soldering the chain to the correct length. Most chains are not easily made longer. Some chains are more difficult to alter, either to shorten or lengthen. Shortening chains you'll end up with the cut off segment that only has scrap value and his usually not worth what it has cost the jeweler to shorten the chain; all the costs of making a bit of gold into chain has been lost. However, the GOOD NEWS is that you have the exact length you wanted!