Reynolds Number Calculator
Calculate reynolds number instantly in your browser — the published formula, worked locally with no data sent anywhere.
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What this tool does
Calculate reynolds number instantly in your browser — the published formula, worked locally with no data sent anywhere. The 2300 / 4000 thresholds are for flow inside pipes, with L = pipe diameter. Flat plates and other geometries use different transition values (about 5×10⁵ for a smooth plate).
How to use the Reynolds Number Calculator
- Enter or select fluid density ρ (kg/m³ — water 1000, air 1.225).
- Enter or select flow velocity v (m/s).
- Enter or select characteristic length l (m — pipe diameter for pipes).
- Enter or select dynamic viscosity μ (pa·s — water 0.001, air 1.81e-5).
- Read the calculated result; change any measurement to compare alternatives.
Formula
Reynolds number Re = ρ × v × L / μ — the ratio of inertial to viscous forces in a flow.
- rho
- Fluid density ρ (kg/m³ — water 1000, air 1.225)
- velocity
- Flow velocity v (m/s)
- length
- Characteristic length L (m — pipe diameter for pipes)
- mu
- Dynamic viscosity μ (Pa·s — water 0.001, air 1.81e-5)
The 2300 / 4000 thresholds are for flow inside pipes, with L = pipe diameter. Flat plates and other geometries use different transition values (about 5×10⁵ for a smooth plate).
Worked example
For reynolds number calculator, the following measurements illustrate the exact method: Fluid density ρ (kg/m³ — water 1000, air 1.225): 1000; Flow velocity v (m/s): 2; Characteristic length L (m — pipe diameter for pipes): 0.05; Dynamic viscosity μ (Pa·s — water 0.001, air 1.81e-5): 0.001.
Inputs
- Fluid density ρ (kg/m³ — water 1000, air 1.225)1000
- Flow velocity v (m/s)2
- Characteristic length L (m — pipe diameter for pipes)0.05
- Dynamic viscosity μ (Pa·s — water 0.001, air 1.81e-5)0.001
Result
- Reynolds number100,000
- Flow regimeTurbulent — chaotic mixing (for pipe flow)
- Kinematic viscosity ν = μ/ρ (m²/s)0
Results explained
- Reynolds number
- Reynolds number from the formula above. The 2300 / 4000 thresholds are for flow inside pipes, with L = pipe diameter. Flat plates and other geometries use different transition values (about 5×10⁵ for a smooth plate).
- Flow regime
- Flow regime from the formula above. The 2300 / 4000 thresholds are for flow inside pipes, with L = pipe diameter. Flat plates and other geometries use different transition values (about 5×10⁵ for a smooth plate).
- Kinematic viscosity ν = μ/ρ (m²/s)
- Kinematic viscosity ν = μ/ρ (m²/s) from the formula above. The 2300 / 4000 thresholds are for flow inside pipes, with L = pipe diameter. Flat plates and other geometries use different transition values (about 5×10⁵ for a smooth plate).
Frequently asked questions
Reynolds number Re = ρ × v × L / μ — the ratio of inertial to viscous forces in a flow.
The 2300 / 4000 thresholds are for flow inside pipes, with L = pipe diameter. Flat plates and other geometries use different transition values (about 5×10⁵ for a smooth plate).
Every field is labelled with its unit — enter values in exactly the labelled unit and read the result in the labelled output unit. Fields with a unit symbol also support the site-wide imperial/metric switch, which converts before the formula runs.
It uses double-precision arithmetic and the published constants and formulas named on this page. The last displayed digit may be rounded, and real conditions can differ from the idealized model described in the assumptions.
Yes. Every calculation runs entirely in your browser; nothing you enter is uploaded, stored or shared.