In the USA, Karat with a "K" refers to the purity of the gold, and Carat with a "C" refers to the weight of a diamond or gemstone.
Karatage is one of the most important factors to consider when buying gold.
Karatage is often perceived as a seal of quality rather than a mathematical reference to percentage of gold. The U.S. laws mandate that a gold product must be at least 10K Gold to be legally called Gold.
Pure gold is 24 Karat Gold. 24 Karat is rarely used to produce jewelry as gold is a soft metal and would not wear well on a daily basis.
Considered to be the most 'pure' for the production of jewelry, the perception of higher value is real. 18K Gold is, in fact softer than 14K or 10K since 18K is comprised three-quarters (18/24, 75%) of Pure Gold.
Overall 14K is considered the threshold, the standard for karat gold in the US. 14K or .583 is (14/24, 58.3%) Pure Gold.
Truly "Gold: with generally higher strength but lower intrinsic value. 10K or .417 is (10/24, 41.7%) Pure Gold.