if its the weight of concrete/m3 it is 2400 kg/m3.If u want to calculate the reinforcement required it should calculated separately as per the unit,it varies from suppose footing,columns,beams.slabs etc etc.u cannot have a thumb rule for steel calculation as it depends on the type of structure,but as such for a villa type of structure u can take the steel qty as150 kg/m3 of concrete.But better to evaluate the steel as per the section of the member