What is the real value of any money paper say us$ or Saudi ryal?

The real value of the money is always determined through the Federal reserve the State has in exchange against  the paper  money. As money is generally valued in bullion, but it also takes into account, inflation, National Income Index, import- export business and the development in Industry and trade, the State does. Dollar is valued by the Federal reserve of the committee of the Central Bank of USA, after the second world war and industrial revolution in USA, the growth of the Economy was tremendous , there were oil, manufacture and industry, the bankers like Gold man sachs , jp morgan , who were also the members of the federal committee, increased the value of the dollar by listing the oil cartels in the stock exchange and traded it in high value, which made dollar automatically go up. However, when oil was discovered in Saudi, the scenario changed and USA got an option to buy oil from Saudi  and the value of the dollar was more hyped due to such trade. However, through a mutual understanding, the exchange rate to dollar was kept stagnant for OPEC countries. As of now, dollar and british pound are the most valued currency for any exchange in any platform either it's for real cross-border trade or exchange indices. 

No financial or other asset has any real value.   Something is worth only as much as somebody is willing to pay for it.

Paper money is a medium of exchange.  Insofar as it has any value, that value lies in the confidence that people have in the system that supports it.  As long as there is confidence in the system (and therefore the money) it has value, but if that confidence is lost the money is worthless.

The real value of any paper money is its Purchase Power. 

The amount of paper money printed by a country is determined by many things including resources the country has and the prices of commodities. Prices of commodities are determined from the equilibrium point (intersection point) of demand and supply curves.

If you can by same commodity in a country with with less money than other country, its money value is greater. So the real value of paper money is its Purchasing Power.