Okay, let's first put this reply in context. I do not believe that an FMU-based fueling scheme is optimal, necessary, or even wise. Modern electronic fuel injection permits the fuel curve to be dialed in with computer precision. A rising rate pressure regulator, on the other hand, creates the fuel curve mechanically. At best, it is a compromise. This method can certainly work, but never as precisely as an OEM-"proper" set up with bigger injectors, appropriate pressure, and software that is carefully tuned for the engine and its operating parameters.
I'd look to EIP for particular guidance about working with this FMU. They're clearly the masters of this technique whether I agree with their methods or not.
With that said, let's directly address your question. Your max fuel requirement is tied directly to the power that you intend to support. So, how much output are we talking about here? (Please clarify whether you're talking about whp or bhp/chp.) What compression ratio do you have? What octane level do you intend to tune with? Do you have a wideband to tune with?
Or... are you simply asking what fuel pressure in psi corresponds to a given pressure expressed in bar? Remember that 1bar = 14.5psi. And... considering that a fuel pressure gauge will cost you $25 or less, there's absolutely no reason not to have one (assuming you don't already).