Necklace chains come in many different lengths and most commonly measured in inches in even numbers with chain completely extended (or clasped with measurement simply doubled). Depending on the style you're going for and what works best for your body type and wardrobe you have several choices so I understand how it can be overwhelming.
Here's a quick an easy guide to find what necklace length works best for you:
14 inches - Fits tightly around the neck and is best worn with open neck clothing such as scoop necks, off the shoulder or boatneck
16 inches - Fits right at the base of your neck and goes well with most clothing necklines
18 inches - Fits just at or right below the collarbone - This is the most common size chain length because it goes with everything!
20 to 24 inches - Sits between collarbone and bust and goes well with casual necklines and business blouses
28 to 36 inches - Sits on the bust or just below and is best suited for high necklines
36 to 42 inches - Rope or wrapped to sit on or just below the bust and worn with high necklines and evening wear
There may be variations in fit depending on your body type that require you to size up or down a few inches but a great thing about custom jewelry is you can request any length that works best for you. If you need a custom sized necklace please don't hesitate to reach out to me.