To my knowledge, at least one configuration of an impeller diameter at one speed would have to be measured empirically (the manufacturer will have this info, probably on-line, and definitely free for the asking). Then, you can use similarity laws to determine theoretical flows, TDH, NPSH, BHP for other sizes.
The only formula I am aware of a formula which would give you this is one which involves specific speed (n-sub-s). But this again must come from the manufacturer.
