Reynolds Number Calculator

Absolute Viscosity

density (kg/m3, lbm/ft3)
velocity (m/s, ft/s)
hydr. diameter (m, ft)
absolute (dynamic) viscosity (N.s/m2, lbm/s.ft)

Kinematic Viscosity

velocity (m/s, ft/s)
hydr. diameter (m, ft)
kin. visc. (m2/s, ft2/s))

The Reynolds number (Re) is used to predict similar flow patterns in different fluid flow situations.

The Reynolds Number formula

Re = (ρ u2) / (μ u / L) = ρ u L / μ = u L / ν


Re = Reynolds Number (non-dimensional)

ρ = density (kg/m3, lbm/ft3)

u = velocity based on the actual cross section area of the duct or pipe (m/s, ft/s)

μ = dynamic viscosity (Ns/m2, lbm/s ft)

L = characteristic length (m, ft)

ν = kinematic viscosity (m2/s, ft2/s) provides you helpful and handy calculator resources.