Plumbing & Fluid

Reynolds Number Calculator

Calculate Reynolds number, velocity or viscosity with circular-pipe regime context. Compare SI/US results and review the method, assumptions and related references below.

Change any input to update the calculation. Unit changes preserve the physical quantity.

CALCULATION SETUP

Inputs

Solve forPreset

Circular-pipe inside diameter

Need an input value?

Pipe Size & Schedule Chart ↗

Mean velocity

Viscosity entry

Kinematic viscosity

Need an input value?

Water Properties Table ↗Pipe Reynolds Number Reference ↗

Fluid density

Need an input value?

Water Properties Table ↗Pipe Reynolds Number Reference ↗

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YOUR CALCULATION

Results

Reynolds number

49,800.7968

Velocity

1 m/s3.2808 ft/s

Kinematic viscosity

1.004 cSt1.004e-6 m²/s

Dynamic viscosity

1.002 cP0.001 Pa·s

Volume flow

1.9635 L/s117.8097 L/min7.0686 m³/h31.122 GPM (US)4.1604 CFM

Full circular pipe bore with flow and mean velocity · schematic, not to scale

Calculation breakdown

Circular-pipe regime convention: Turbulent range

Assumptions & checks

The laminar/transition/turbulent labels use common full circular-pipe conventions, not universal thresholds for all geometries. Fluid properties depend on temperature.

Formula

Calculate Reynolds number, velocity or viscosity with circular-pipe regime context

Re=vD/ν=ρvD/μ; ν=μ/ρ; circular-pipe volume flow Q=vπD²/4. Worked example: 50 mm inside diameter, 1 m/s and 1.004 cSt gives Re≈49,801; circular-pipe flow is 1.9635 L/s.

Worked example

Using the default values shown in the calculator, the same formula gives the following result. This is a quick sanity check for the calculation, not a design recommendation.

Inputs

Circular-pipe inside diameter: 50 mm
Mean velocity: 1 m/s
Viscosity entry: Kinematic viscosity
Kinematic viscosity: 1.004 cSt
Fluid density: 998 kg/m³

Result

Reynolds number: 49,800.7968
Velocity: 1 m/s
Kinematic viscosity: 1.004 cSt
Dynamic viscosity: 1.002 cP
Volume flow: 1.9635 L/s

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Technical references for this calculation

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Frequently asked questions

What does this result tell me?

The laminar/transition/turbulent labels use common full circular-pipe conventions, not universal thresholds for all geometries. Fluid properties depend on temperature.

How can I check the calculation?

Worked example: 50 mm inside diameter, 1 m/s and 1.004 cSt gives Re≈49,801; circular-pipe flow is 1.9635 L/s. Review each stated input and unit; use project-specific values rather than treating the editable example as a requirement.

Reference data & method sources

NASA Reynolds number
Inertial/viscous ratio Re = velocity × characteristic length / kinematic viscosity.
NIST SI conversion factors
SI/US dimensional conversions. Geometry and energy balances are stated explicitly, not attributed to a design standard.