Here's another perspective. Not mine though.

I have had many ebay members, especially overseas buyers ask me in regards to 9ct gold fineness and its equivalent, weather it is real gold or not, as some overseas buyers have never heard of it. For those of us living in Australia, the UK or other countries of the Commonwealth, 9ct gold is the most common fineness of gold jewellery found on the market. I have listed below all gold finenesses used for jewellery making and their equivalents in percentage.
8ct, 8K or 333 stamped items are 33.3% in gold fineness
9ct, 9K or 375 stamped items are 37.5% in gold fineness
10ct, 10Kor 416 stamped items are 41.6% in gold fineness
14ct, 14K or 585 stamped items are 58.5% in gold fineness
18ct, 18K or 750 stamped items are 75% in gold fineness
21ct, 21K stamped items are 87.5% in gold fineness
22ct,22K or 916 stamped items are 91.6% in gold fineness
23ct, 23K or
965 stamped items are 96.5% in gold fineness
24ct, 24K or 999 stamped items are 99.9% or described as PURE gold
Also, some buyers are confused in regards to the abreviation of ct instead of K. Carat- ct - is a term actually used for weight, where as Karat - K - refers to the gold fineness. Am not exactly sure, why the Commonwealth countries use ct instead of K or even kt . But I guess it must have something to do with why British write colour and Americans write it color
9ct gold is the most common karatage used in Australia, due to being more affordable than 18ct gold. Also it is more durable, as it is harder due to the other metals mixed into the alloy to obtain 375 fineness of 9ct gold. The colour of the gold seems to be more appealing to the modern woman, too, as it is not that buttery yellow like some asian jewellery is. Though I must add, that the appeal of 24ct Pure Gold jewellery is also awe-inspiring. Any of you that had the chance to view a pure gold piece of jewellery might agree, that the gold colour of those items is superb - well, it is pure gold after all. But due to its softness pure gold jewellery is not very durable, as it bents and dents easily.
I just thought I also point out that some karatages of gold are only available in some parts of the world.
8ct gold, which is usually stamped 333 is as far as I know only used in Europe- especially Germany
10ct gold is widely used in the US and Canada, but as manufacturers or wholesalers can market there items anywhere nowadays, it is also seen in other parts of the world
21ct gold items are mostly produced in Arab countries, and usually the stamp is in Arabic numarals, so you might see instead of 21ct a vertical line and a V (looks like lV)
23ct is widely spread in Asia, though more common in Thailand, as other asian countries prefer either pure 24ct gold, or 22ct gold
Hope this guide has been helpful ! If it has, please indicate so below, and if you have any questions, you are always welcomed to contact me through ebay anytime.