Compute Reynolds number for pipe flow, non-circular ducts using hydraulic diameter, and external flow cases. Includes viscosity modes, unit conversion, and regime guidance.
ReLaminar/TurbulentHydraulic DiameterViscosity
Reynolds Number (Re) & Flow Regime Estimator
Calculate Re using velocity and characteristic length with either dynamic viscosity μ and density ρ or kinematic viscosity ν. Supports internal and external flow cases.
Reynolds Number (Re)
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Flow Regime (Pipe Guideline)
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Equivalent ν (m²/s)
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Inputs in SI
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Equation Used
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Notes
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Pipe regime thresholds are rules of thumb for fully developed internal flow. Transition depends on disturbances, roughness, and entrance effects.
Hydraulic Diameter (Dh)
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Reynolds Number (Re)
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Pipe-Regime Guideline
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Equivalent ν (m²/s)
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Inputs in SI
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Equation Used
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Hydraulic diameter Dh = 4A/P applies pipe-style Re to non-circular passages, including rectangular ducts and partially filled channels.
Reynolds Number (Re)
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Interpretation
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Equivalent ν (m²/s)
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Inputs in SI
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Case
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Equation Used
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External flow transition depends on geometry and disturbances. Use Re as an indicator for selecting correlations (drag, heat transfer, boundary layer, etc.).
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V
L
ν
Re
Regime (Pipe Guideline)
Batch mode uses Re = (V·L)/ν with your chosen units. Pipe regime labels are applied as a convenience when L is a diameter/hydraulic diameter.
