How it works
Reynolds number Re = density × mean speed × pipe diameter / dynamic viscosity.
Input definitions
- Density (kg/m³)
- Enter the value in the labeled unit.
- Mean speed (m/s)
- Enter the value in the labeled unit.
- Internal diameter (m)
- Enter the value in the labeled unit.
- Dynamic viscosity (Pa·s)
- Enter the value in the labeled unit.
A worked example
- Density (kg/m³)
- 1000
- Mean speed (m/s)
- 1
- Internal diameter (m)
- 0.05
- Dynamic viscosity (Pa·s)
- 0.001
Assumptions & limits
Circular-pipe regime thresholds are approximate and depend on disturbances. Use dynamic viscosity in Pa·s, not kinematic viscosity.
Sources & review
Maintained by AnsRio. Methods and examples use automated checks; this does not imply independent professional certification.
Method updated 2026-10-17. Content checked against the stated method and examples. Our verification approach.
Common questions
Should I enter dynamic or kinematic viscosity?
Use dynamic viscosity in Pa·s for Re=ρvD/μ. If you have kinematic viscosity ν in m²/s, convert using μ=ρν before entering it.
Which units should I enter?
Use the units written in each input label. These formulas assume idealized conditions; changing to centimetres, litres or kilopascals without conversion changes the meaning of the result.
How does the Pipe Reynolds number tool work?
Reynolds number Re = density × mean speed × pipe diameter / dynamic viscosity.
What are the assumptions and limits of Pipe Reynolds number?
Circular-pipe regime thresholds are approximate and depend on disturbances. Use dynamic viscosity in Pa·s, not kinematic viscosity.