What is Reynolds Number?

Reynolds Number is dimensionless quantity that is proportional to the ratio of inertia forces to viscous forces in a flow system. The proportional constant is the characteristic length of the system. For Pipe Reynolds Number, the characteristic length is the pipe diameter. Reynolds Number is a convenient parameter by which to compare different flow systems.

Pipe Reynolds Number can be found by using the following equations:

R = [DV/v]r

or [DV /u]


R = Reynolds Number
D= inside pipe diameter (ft or m)
V= fluid velocity (ft/s or m/s)
v = kinematic viscosity (ft2/s or stokes)
r = fluid density (lb/ft3 or kg/m3)
u = absolute viscosity (lb/ft s or poises)

Many convenient hybrid forms of the Reynolds Number equation exist. One such equation for liquid is:

R = C*Q(GPM) v(cSt)

Where C is the constant