How to set a minimum wage How does a country set an optimum minimum wage, i have went through loads of website but none of them give me a satisfied answer. For example, median of a country's income, percentage of GDP and such seem too shallow and unfair as a medium of calculation.
What criteria define an optimum minimum wage? Is there even such a thing?

The reason why you haven't found a satisfactory answer is that there isn't one. There are several and depending on who you ask you will get a different answer.

Some people will say that the optimum minimum wage is 0 and that the state should note interfere in the matter. Laissez-faire. 

Some people wants the minimum wage to cover basic living expenses. What that entails varies widely but is usually connected to the general economic level of the country. In some countries it covers only the cost of basic food for 1-2 people. In others it covers rent, utilities, food, a tv, a mobile phone.

Some people want the minimum wage to be as high as possible. Some unions.