Reynolds Number Calculator
Determine whether flow in a pipe or duct is laminar, transitional, or turbulent
Calculator
Enter the fluid and pipe parameters below to calculate the Reynolds number (Re).
About the Reynolds Number Calculator
The Reynolds Number Calculator helps you determine whether fluid flow in a pipe, duct, or channel is laminar, transitional, or turbulent. By entering the flow velocity (V), pipe diameter (D), and fluid properties such as density (ρ) and dynamic viscosity (μ), this tool instantly calculates the Reynolds number (Re). It is ideal for fluid mechanics students, engineers, and HVAC or hydraulic designers working with internal flow systems.
What You Can Calculate
- Reynolds Number (Re): A dimensionless value used to characterize flow behavior in pipes and ducts.
- Flow Regime: Determine whether the flow is laminar (smooth), transitional, or turbulent (chaotic).
- Effect of Fluid Properties: Understand how viscosity and density influence flow patterns and resistance.
Formulas Used in the Calculator
The calculator applies the classical Reynolds number equation used in fluid dynamics:
- Re = (ρ × V × D) / μ
- where:
- ρ = Fluid density (kg/m³)
- V = Flow velocity (m/s)
- D = Pipe or duct diameter (m)
- μ = Dynamic viscosity (Pa·s)
Based on the computed Reynolds number, the flow is classified as:
- Laminar flow: Re < 2300
- Transitional flow: 2300 ≤ Re ≤ 4000
- Turbulent flow: Re > 4000
How to Use the Calculator
- Enter the flow velocity (V) and select the appropriate unit (m/s, cm/s, or ft/s).
- Provide the pipe or duct diameter (D) with the desired unit (m, cm, mm, or in).
- Input the fluid density (ρ) and viscosity (μ) values using standard SI or customary units.
- The calculator instantly displays the Reynolds number (Re) and identifies the flow regime.
Applications of Reynolds Number Analysis
The Reynolds number is a fundamental concept in fluid dynamics and heat transfer. It helps engineers evaluate flow behavior in pipelines, HVAC ducts, reactors, pumps, and open channels. Determining the flow regime is critical for pressure loss estimation, energy efficiency, and flow control system design. Understanding whether the flow is laminar or turbulent also aids in selecting suitable flow meters, valves, and pipe materials.