Reynolds number compares inertial and viscous effects in a flow.
Difficulty
Intermediate
Read time
5 min
Prerequisites
Basic algebra and consistent SI units
Source
OpenStax, College Physics 2e, §12.5 (Paul Peter Urone and Roger Hinrichs)Textbook reference retained from the OpenFormulaGraph dataset; adaptation credits and license are provided below.
Adapted from OpenFormulaGraph, under CC BY 4.0.
FormuLab adapted the notation, explanations, assumptions, and topic placement, and expanded the numerical check into a worked example.
Reynolds number compares inertial and viscous effects in a flow. It helps characterize flow regimes, but transition criteria depend on geometry and disturbances. This form uses pipe diameter as the characteristic length.
| Symbol | Meaning | Units |
|---|---|---|
| Reynolds number | ||
| Fluid density | ||
| Mean flow speed | ||
| Internal pipe diameter | ||
| Dynamic viscosity |
Characterize the relative importance of viscous effects.
Compare flows using a dimensionless parameter.
Water with density 1000 kg/m³ and dynamic viscosity 0.00100 Pa·s flows at mean speed 0.500 m/s through a 0.0200 m diameter pipe. Find Reynolds number.
Textbook reference retained from the OpenFormulaGraph dataset; adaptation credits and license are provided below.
Adapted from OpenFormulaGraph, under CC BY 4.0.
FormuLab adapted the notation, explanations, assumptions, and topic placement, and expanded the numerical check into a worked example.
Assumptions
FormuLab is a study reference. Verify formulas, units, assumptions, and course-specific conventions before relying on them.
© 2026 FormuLab. All rights reserved.