Pipe Flow Calculations Forum

I've been working through the theory of the orifice plate to input the equation into my own program but hit a snag.
It appears I need the Reynolds number to for the equation, but to calculate it I need velocity, which seems silly because if I have velocity I could calculate the mass flow rate easily from it.
Other than that portion I have the rest of the equation ready.

Is this an iterative problem where it is best guess at first than perform it several times until you get the same result?

You are right.
you can try also orifice free calculator