The karat system is used most often in jewelry. But many 1-ounce bullion coins are 24 karat - sometimes called 24 carat - which means they are 99.99% pure gold or better. These 24 karat gold coins include UK Britannias, American Buffalos, Australia's Kangaroo, Austrian Philharmonics, and Canadian Maples.
While the 24 karat gold coins have what's known as 9999 millesimal fineness, other very popular coins like the British Sovereign and the American Eagle, are 22 karat = 0.9167 fine.
Large wholesale bullion bars must be 995 parts per 1,000 pure gold. But here, in the professional market, you only ever pay for the fine gold content. No one ever pays for the other 5 parts per thousand.