Reynolds Number Calculator

How the reynolds number calculator works

Dynamic-property mode uses Re = density × velocity × characteristic length ÷ dynamic viscosity. Kinematic mode uses Re = velocity × characteristic length ÷ kinematic viscosity. With the stated SI units, either ratio is dimensionless. Zero velocity or characteristic length gives zero.

Properties must match fluid temperature, pressure and composition. Dynamic and kinematic viscosity have different physical dimensions and cannot be interchanged without density. Characteristic length depends on geometry. No universal transition threshold, friction factor, turbulence certainty or acceptable flow/design condition is assigned here.

Quantities use the stated units and finite bounded inputs. Whole purchases round up under the documented model; cost components round half-up to cents before totals are summed. Undefined ratios stay unavailable. π and logarithms use normal numeric precision. Display rounding does not alter the entered assumptions.

Worked example

At 1,000 kg/m³, 1 m/s, 0.1 m characteristic length and 0.001 Pa·s, Re is 100,000. The equivalent entered kinematic viscosity 0.000001 m²/s gives the same ratio. Doubling velocity gives Re 200,000.

Sources and assumptions

The source material explains the underlying calculation or pricing structure. Entered prices, costs, schedules and scenario choices are your assumptions; this tool does not obtain supplier quotes or predict actual results.

• NIST SI Appendix B.9 conversion factors
• DOE Pumping System Performance sourcebook