Reynolds Number Calculator (Re=ρvD/μ, Laminar/Transitional/Turbulent)
Compute the Reynolds number Re = ρ·v·D/μ (dynamic viscosity) or Re = v·D/ν (kinematic viscosity, ν = μ/ρ) and classify the flow regime: Re < 2300 laminar, 2300 ≤ Re < 4000 transitional, Re ≥ 4000 turbulent. Diameter accepted in m/cm/mm. In dynamic mode the kinematic viscosity ν = μ/ρ is also returned. For internal pipe flow and general fluid-mechanics regime analysis.
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Key facts
Category
Math & Numbers
Input types
select, number
Output type
json
Sample coverage
4
API ready
Yes
Overview
Calculate the Reynolds number for pipe flow and fluid-mechanics analysis using dynamic or kinematic viscosity. Enter velocity, diameter, and the required viscosity values to get Re, the flow regime, and, in dynamic mode, kinematic viscosity.
When to use
Classify an internal pipe flow as laminar, transitional, or turbulent.
Compare flow regimes for different fluid velocities, diameters, or viscosities.
Use a hydraulic diameter with fluid properties for general flow-regime analysis.
How it works
1Choose Dynamic mode and enter density, velocity, diameter, diameter unit, and dynamic viscosity, or choose Kinematic mode and enter velocity, diameter, and kinematic viscosity.
2The calculator converts the diameter from meters, centimeters, or millimeters to meters.
3It calculates Re using Re = ρvD/μ in Dynamic mode or Re = vD/ν in Kinematic mode.
4The result classifies the flow as laminar below 2300, transitional from 2300 to below 4000, or turbulent at 4000 and above.
Use cases
Pipe and duct flow checks using a diameter or hydraulic diameter.
Fluid-mechanics coursework and engineering calculations.
Evaluating how viscosity and flow speed affect laminar or turbulent behavior.
Examples
1. Water flow in a 50 mm pipe
Fluid engineer
Background
An engineer is checking the flow regime of water moving through a 50 mm pipe at 2 m/s.
Problem
Determine the Reynolds number and identify whether the flow is laminar, transitional, or turbulent.
How to use
Select Dynamic mode and enter density 1000 kg/m³, velocity 2 m/s, diameter 0.05 m, and dynamic viscosity 0.001 Pa·s.