Purity Measure is a term used to describe the measurement of the amount of gold in an item. The most common way to measure purity is by using the Karat system, which is a unit of measurement that indicates the proportion of gold in an alloy. A Karat is equal to 1/24th of the total weight of the alloy, and is represented by the number of karats followed by the letter 'K'. For example, 24K gold is pure gold, while 18K gold is 75% gold and 25% other metals.