Reynolds Number Calculator

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Sets the transition thresholds. Internal pipe flow transitions near Re 2300-4000; a flat plate near 500,000.
Pick a fluid to auto-fill density and viscosity, or choose Custom to type your own.
Dynamic viscosity. Water at 20 C is about 0.001 Pa.s, air about 1.8e-5 Pa.s.
Pa.s
For a full round pipe, average velocity = flow rate / cross-section area.
Average speed of the fluid relative to the surface.
m/s
Pipe inner diameter for internal flow, or chord / plate length for external flow. Also the diameter used for the flow-rate option.
m
Reynolds numberTurbulent flow
99,621

Dimensionless ratio of inertial to viscous forces.

Flow velocity used2m/s
Dynamic viscosity (mu)0.001002Pa.s
Kinematic viscosity (nu)0.000001m2/s
Max laminar velocity (this L)0.046m/s
99,621
Laminar<2300Transitional2300-4000Turbulent4000+

Re ~ 99,621, the flow is turbulent.

  • Re is the ratio of inertial forces (rho*v*L) to viscous forces (mu); it is dimensionless.
  • For pipe (internal flow), the laminar limit is about Re 2,300.
  • Below about 0.046 m/s the flow at this length stays laminar.

Next stepThese thresholds are for pipe (internal flow); switch the geometry selector if your case is different.

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