Reynold Number Calculator

Blog post description.

Wiratama

11/15/20251 min read

Reynolds Number – Definition

Reynolds number (Re) is a dimensionless parameter that indicates the flow regime of a fluid inside a pipe or around an object. It describes whether the flow is laminar, transitional, or turbulent, making it one of the most important concepts in fluid mechanics.

Background Theory

Reynolds number is defined as:

Where:

  • ρ = fluid density (kg/m³)

  • V = flow velocity (m/s)

  • D = characteristic length (typically pipe diameter, m)

  • μ = dynamic viscosity (Pa·s)

Flow regime thresholds:

  • Laminar: Re < 2,300

  • Transitional: 2,300 < Re < 4,000

  • Turbulent: Re > 4,000

Reynolds number compares inertial forces to viscous forces, helping assess mixing, pressure drop, and friction behavior.

How This Calculator Works

The calculator evaluates the Reynolds number by:

  1. Taking inputs for density, velocity, diameter, and viscosity

  2. Applying the Reynolds number formula

  3. Displaying the resulting Re value instantly

This allows quick assessment of flow behavior for piping systems, HVAC ducts, heat exchangers, and general fluid mechanics problems.