Science & Engineering

Reynolds number.

Estimate whether internal pipe flow is laminar, transitional, or turbulent from the dimensionless Reynolds number.

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Reynolds number formula

Reynolds number compares inertial effects with viscous effects: Re = ρvL ÷ μ. For a round pipe, L is normally the inside diameter. As a quick guide for internal pipe flow, values below about 2,300 are laminar, 2,300–4,000 are transitional, and values above about 4,000 are turbulent. The exact transition depends on geometry, roughness, and disturbances.

Reference: OpenStax, Viscosity and Turbulence and NASA Reynolds-number analysis.

Engineering note

This is a dimensionless screening calculation, not a substitute for a detailed fluid model or design standard.