how much karats are in a 5.5mm gold chain?

The length of the chain is not what determines karats. Karats are a measurement of how pure the existing gold is in any object. If an object is composed of 24 karat gold, it is 100% pure gold. If it's 12 karat, that means that only half of the metal is pure gold, and the other half is various other alloys or substances.

Gold chains don't have Karats. Diamonds have them.

idk