According to the national standard GB11887-89, the gold content per k is 4.166%.
The gold content of k gold is respectively (national standard in brackets) :
10k=10*4.166%=41.660%（417‰）
12 k = 12(500‰)* 4.166% = 49.992%
18K=18*4.166%=74.998%（750‰）
20k=20*4.166%=83.320%（833‰）
24 k = 24(999‰)* 4.166% = 99.984%