Hi, is it possible to post back, and let us know exacxtly what you are trying to do? It is quite hard to answer a question like this, as the answer will be different depending on whether you have a gas in a gas, a liquid in a liquid, a solid in a gas etc, and what the different components are.
Also, Nm³ can mean different things, as the "N" is a standard metric symbol, but it means newtons, which is not what it will mean in your application. Sometimes it is used to mean normal cubic meter, but the "normal" temperature and pressure change from industry to industry.