how to work out cubic flow with only pressure

What formula do i need to convert gas flow across an orifice plate , the oriface plates vary but say a 40 cube plate. I have a digital monometer so i can use most pressures. which would be the best/easiest pressure to use to convert to nm3/hr. thanks guys

PLEASE HELP! any ideas people? there must be an easy formula where i can TIMES the pressure accross the plate by size of plate etc or something im just too silly to work it out? with the result giving me nm3/hr thanks..

[JohnS]

Originally Posted by Unregistered

PLEASE HELP! any ideas people? there must be an easy formula where i can TIMES the pressure accross the plate by size of plate etc or something im just too silly to work it out? with the result giving me nm3/hr thanks..

I think "easy" is the problem. Lots of factors have to be considered. Here's two links that may help.
http://en.wikipedia.org/wiki/Orifice_plate
http://www.pipeflowcalculations.com/orifice/

The second one is more detailed. Follow the links at the bottom of the page above for more on each topic.