Reynolds Number Calculator
Calculate Reynolds number with dynamic or kinematic viscosity and mixed speed/length units. Optionally compare against a stated circular-pipe reference convention.
YOUR CALCULATION
Result
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Calculation steps
Work through one step at a time or reveal the complete calculation. The steps use your current inputs.
How to calculate
Convert speed, length and viscosity to SI units. Divide dynamic viscosity by density if that input form is selected. Calculate the dimensionless ratio of speed times characteristic length to kinematic viscosity.
Re=ρVL/μ=VL/ν; ν=μ/ρ
Worked example
Mean speed 1 m/s, pipe diameter 10 mm, density 1000 kg/m³ and dynamic viscosity 1 mPa·s give ν=1 mm²/s and Re=10000. Direct kinematic viscosity 1 cSt gives the same result.
Assumptions and input details
Use fluid properties at the operating temperature and a characteristic length appropriate to the geometry. This tool does not look up temperature-dependent properties. 1 cP=1 mPa·s=0.001 Pa·s; 1 cSt=1 mm²/s=10⁻⁶ m²/s. Circular-pipe reference labels use Re<2300, 2300≤Re≤4000 and Re>4000; these are reference ranges, not a guarantee of an observed flow state. Other geometries receive no automatic classification. The model assumes an appropriate continuum/Newtonian viscosity description and does not calculate pressure drop, roughness, entrance length, compressibility or non-Newtonian behavior. Zero speed gives Re=0 and is labelled no flow.
References: NASA Reynolds number · IIT Patna pipe-flow reference
Unit definitions
Unit selection is independent of language. Each selector contains only units for its physical quantity. Calculations use defined base units internally.
Choose from 23 length definitions, including explicitly labelled regional measures. Area conversions square the length factor; geometric volumes cube it.
Regional measures are not interchangeable merely because their names look similar. This is a documented selection, not a claim to include every historical unit.
NIST measurement tables · Japanese traditional units · Mainland China and Hong Kong unit distinctions
Using this calculator
Can I enter my own problem?
Yes. Replace the example values with your own inputs. The result, calculation steps, tables and applicable diagrams update from those inputs. Blank or invalid values clear the result; example values are never silently substituted for missing inputs.
Are the results exact?
Results use floating-point arithmetic and displayed rounding. Read the formula, assumptions and any stated data precision before interpreting the result.
Is my input uploaded?
The calculation runs in your browser. No account, file upload or external AI service is required. Inputs are not saved between page reloads.
Convert volumetric flow and average speed in a full circular pipe. Calculate mass flow and the time to fill an entered volume.
Find density, mass or volume from the other two values. Choose international and regional units and inspect the formula and unit-conversion tables.
Convert pressure across SI and other common units. Distinguish absolute and gauge readings using a reference pressure you enter, and compare both in a unit table.
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