Karat is the standard of measuring the purity of the gold. Since gold is soft it is treated with alloy to make it hard for crafting jewelry. Normally, copper, silver and zinc are used as alloy. By comparing the percentage of gold to its alloy you can determine the purity. In US and Canada, gold jewelry is available in 10K, 14K or 18K, where 24 karat is pure gold. An 18K ring comprises of 18 parts gold and 6 parts alloy. So, you will get the price of the 18k gold only.