Free · Physics models
Flow Reynolds Number and Viscosity
Compare inertial and viscous flow scales using density and dynamic viscosity or kinematic viscosity.
- Formula & worked example
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Calculator inputs
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How to use this calculator
- Enter the known values in the units shown. Results update as you type.
- Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
- Use the worked example to check the method. Reset restores the starting fields.
Private by default
Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.
Formula and method
At 2 m/s over 0.1 m with density 1,000 kg/m³ and dynamic viscosity 0.001 Pa·s, Re is 200,000.
Re = ρ v L/μ = v L/ν; ν = μ/ρ.
Worked example
Enter these known values and leave the other values blank.
- Fluid velocity
- 2 m/s
- Characteristic linear dimension
- .1 m
- Fluid density
- 1000 kg/m³
- Dynamic viscosity
- .001 kg/(m⋅s)
- Kinematic viscosity
- 0.000001 m²/s
- Reynolds number
- 200000
Assumptions and limitations
- Positive characteristic length and speed are required. Use the geometry’s appropriate length scale, such as hydraulic diameter.
- Fluid properties depend on temperature and pressure; preset values are illustrative.
- Laminar/turbulent thresholds are geometry dependent; a Reynolds number alone does not provide a universal classification.
- Enter known quantities and clear the unknown to use available inverse branches. Locks retain supplied values. Consistency messages cover fully visible equations; identities with hidden dependencies may require a manual consistency check. Preset values are illustrative approximations, and unit selectors preserve the underlying quantity.
Common questions
How do I solve for a different quantity?
Clear that quantity and supply enough independent known values. Some outputs are one-way or tied to a selected preset, so they cannot determine every input.
References
The calculation equations, inverse formulas, units, and input rules were imported from this source. Bookify provides the interface and equation solver.