Pipe flow calculators

Reynolds number calculator


Calculator Description

With Reynolds number calculator you can determine ratio of viscous to inertial forces in fluid flow. If that ratio is low than flow is laminar, but if it is high, than flow is turbulent.

  • Calculate:

    • Reynolds number
    • Flow rate
    • Pipe diameter
  • Input:

    • Pipe diameter
    • Fluid viscosity
    • Flow velocity
    • Gas pressure
    • Gas temperature

Calculator Features

  • Applicable for liquids and gases
  • Gas state equation used for density calculation

Reynolds number named after Osborne Reynolds (1842 – 1912), gives relation between inertial and viscous forces of fluid flow. If inertial forces (flow rate) are much bigger and Reynolds number is higher than critical, Re>2320, turbulent fluid flow will occur and if viscous forces are big enough in compare to inertial (flow rate), Reynolds number is lower than critical, Re<2320, laminar fluid flow character will occur.

For calculation of Reynolds number in closed pipe fluid flow mean velocity, fluid viscosity and internal pipe diameter should be known. Reynolds number is proportional to fluid flow mean velocity and pipe diameter and inversely proportional to fluid viscosity.

With Reynolds number calculator you can analyze what makes fluid flow regime laminar and what is needed to force the fluid to flow in turbulent regime. For example - in pipes with very small internal diameter it is more likely to have laminar flow regime with small Reynolds number even for fluid with low viscosity. In fluid flow with temperature change flow regime can change from turbulent to laminar flow regime, as viscosity is changing depending on the fluid temperature.

Calculator can be used for all fluids and flow rates without any restriction. Calculator is applicable for fluid mixtures also, but viscosity of mixture must be entered.


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If you would like to use the calculator, but actually can't see the blue CALCULATOR button in the upper left part of the page than please read instructions.

Q: Calculate Reynolds number for flow in closed round pipe. Flow velocity is 2 m/s, pipe inside diameter is 100 mm and fluid viscosity is 0.00001 m2/s

A: Calculation setup:
Input values:
D = 100 mm
V = 2 m/s
ni = 0.00001 m2/s

Q: Calculate Reynolds number for water flow in closed round pipe. Flow velocity is 2 m/s, pipe inside diameter is 50 mm

A: Calculation setup:
Input values:
D = 50 mm
V = 2 m/s
ni = 1.006 mm2/s

Q: Calculate Reynolds number for water flow in small diameter closed round pipe. Flow velocity is 1 m/s, pipe inside diameter is 2 mm

A: Calculation setup:
Input values:
D = 2 mm
V = 1 m/s
ni = 1.006 mm2/s

Reynolds number calculator is based on following formula:

Read more about used theory on flow in pipes page.

If you experience problems with calculator start try to find answers on instructions page.

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