Density of the gas cannot be calculated based on only composition and molecular weight. For calculation, temperature and pressure of the gas will be needed apart from composition (identification of the gas). See attached a sample calculation of natural gas density. Similar calculation sheet can be developed for LD gas also.

http://www.unitrove.com/engineering/tools/gas/natural-gas-density

Dear SOHAIL AHMAD KHAN  

We have the Molecular weights / Temperature / and pressure of the gases 

and we need The Density of the LD Gases Not Natural gases  

(LD gas  or Converter Gas  is produced during the process of steel making in Basic oxygen furnace)

the above link calculator will works for only natural gases 

We need Method of Calculation Not Calculator 

LD gas contains 

CO2 CO, CH4 & Other higher Hydrocarbon(Alkane Alkene,Alkynes), nitrogen , Oxygen , Hydrogen , H2S, NH3, 

 with Different Ratio its depends upon the process

Dear Mr. Kuppu Samy,

The LD Gas before it enters the cleaning system is on dry basis i.e it contains only CO, CO2, N2 and traces of O2. And after the cleaning system it contains in addition H2O.

You need to know the composition of the Gas based on the O2 flow rate and the type of Converter i.e. whether it is Suppressed combustion system (and air factor) or a full combustion system. Now if you calculate the gas composition (Vol Basis) , multiply it by the molecular weight of each component and then add it. The results of addition is divided by 22.4 to get the density in kg/Nm3.