Look in a fluid dynamics book. You may have to turn it around, and look
for the head loss in a pipe given the velocity, then solve for velocity
from pressure.
Don't expect much precision -- fluid dynamics depends on a number of
hard-to-control variables.

How is "resistivity" defined? If it's given as (head loss per unit
length)/(flow rate), just plug in the numbers, but be aware it's a
fiction. "Resistivity" so defined depends on flow rate, pipe diameter,
boundary layer thickness, number of bends, bend radius, .... There's a
lot of theory behind fluid dynamics, but a lot of empiricism too.
Jerry

--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

Lots depends on whether you are considering a laminar or a turbulent
problem (see the text books already referred to, on how to discover
which flow regime you're in).
Very roughly (fully roughly for turbulent flow, in fact... fluid
dynamics joke) relationship between pressure drop and flow (Q) is
related by DP=[K*|Q|]*Q, where K is a constant.
For laminar flow DP=[k]*Q, where k is a different constant. You could
take the [brackets] as analogous to resistance, if DP is analogous to V,
and Q analogous to I.
Works for your old garden hose (which is turbulent at flows beyond a
teaspoon-a-second...)
John

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