passenger in each classes

I want to know how can I evaluate/culculate demand of the passenger in each classses: F-C-Y and also cargo's demand.

My flights currently some of them are full of F-C-Y but some of them full only Y and C gets half and F with 1 or 2 passengers.

I'm using good seat - plane - price for all of my flight. My ORS is standing in the top of page.

You can't calculate demand. You can estimate it, by looking at the size of the airports, possible transfer-connections and competition (via ORS). Anyway, there remains some trial-and-error.

Oh so trail  and error is the final answer!

thank you

That's not what I am saying ... It's research in first place, then good knowledge and finally some trial-and-error. 


how or where do you research the demand for the different classes ?


Not that easy - but basically by assuming that Y:C:F correlates directly for direct connections and looking at the feeder situation. I.e. recognizing, that you regularly don't get as much proper connections within C and F.

Personally, I don't think it's not worth to spent to much time on thinking about demand in C and certainly not in F. I would say, if you have a good understanding in Y and knowledge about the general feeder situation across the classes, you can estimate C and F for many connections. Finally, within these classes it's possibly even more trial and error, as transfer passengers are more likely to take another route. 

Sometimes it´s feasible to operate some aircraft with different seating-configurations to allow a more suitable split of the offered classes of service and capacity/comfort. 

For example, some routes have generally provide a higher demand for Business Class or even First while other markets mostly generate demand for Economy Class.