Reynolds Number Calculator

Calculate Reynolds number for pipe flow from average velocity, pipe inner diameter, and either density with dynamic viscosity or kinematic viscosity. The result also shows a practical laminar, transitional, or turbulent flow guideline.

Need velocity or pipe diameter first? Use the Pipe Velocity and Diameter Calculator.

Input Method

Density and dynamic viscosity

Kinematic viscosity

Input Form

Item	Value	Unit
Average velocity		m/s cm/s m/min m/h ft/s
Pipe inner diameter		m mm cm inch
Density		kg/m³ g/cm³ kg/L g/mL
Dynamic viscosity		Pa·s mPa·s cP P
Kinematic viscosity		m²/s mm²/s cSt St

Calculate

Calculation Result

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Formula Used

Re = ρ u D / μ or Re = u D / ν

• Re: Reynolds number
• ρ: density
• u: average velocity
• D: pipe inner diameter
• μ: dynamic viscosity
• ν: kinematic viscosity

Input Values Converted to SI Units

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Caution Note

The laminar, transitional, and turbulent ranges are general pipe-flow guidelines. Actual flow behavior can differ depending on pipe roughness, inlet conditions, fluid properties, and operating conditions.

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