Various ways of expressing fineness have been used and two remain in common use: millesimal fineness expressed in units of parts per 1,000 and karats used only for gold. Karats measure the parts per 24, so that 18 karat = ⁄ = 75 % and 24 karat gold is considered 100 % gold.
the ratio of pure gold in 24 carat gold is
100 % gold