Length
Where a chain sits depends on body size, neck circumference, pendant use and personal preference. Compare an actual chain or cord at the intended length when possible.
Chain sizing,
before you buy.
A chain specification should include more than length. Width, weight, link construction, metal purity, clasp and whether a piece is solid or hollow can materially change the product and price.
Width
Millimeter width changes the visual presence of a chain. Two chains of the same length can look dramatically different at different widths.
Weight
Gram weight helps describe how much material is present, but construction and alloy matter. Do not infer purity from weight alone.
Construction
Ask whether the piece is solid, semi-solid or hollow and understand the durability and repair implications before purchasing.