Similarly, 999.9 means your gold is 99.99% pure, which means only 0.01% is other metal.

Under this, 999 means that your 24K gold is 99.90% pure and other metal constitutes only 0.1%. Millesimal Fineness, a system denoting the purity of gold, measures the purity by parts per thousand or the percentage of gold, instead of karats. However, in coins and bars the highest level of gold purity is 99.99% while the market standard is 99.5% or 99.9%,” says Gaurav Mathur, Founder & MD, SafeGold, a homegrown digital currency platform. For jewellery, in any case, the purity is 18K or 22K as lower-purity gold is harder and more durable. “The buyer should only invest in the purest quality gold available to them, as the additives such as copper or silver corrode over time, which harms your investment.