Dynamic Viscosity & Reynolds Number Calculator

Fluid Mechanics, Rheology & Dynamic Viscosity Metrology

Dynamic Viscosity (μ or η) quantifies a fluid's internal friction resistance to laminar shear flow under Newton's Law of Viscosity:

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• Universal Dynamic Viscosity Conversion Formulas (ISO Standards)**:

1 Pa·s (Pascal-second) = 1,000 cP (Centipoise) = 1,000 mPa·s = 10 Poise (P)

μ_lb/(ft·s) = μ_Pa·s1.488164 = μ_Pa·s × 0.671969

μ_lb/(ft·h) = μ_Pa·s × 2,419.088

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• Dimensionless Reynolds Number & Flow Regime Thresholds**:

Re = (ρ × v × D) / (μ_Pa)·s

• Laminar Flow: Re < 2,300 (Smooth streamlines, viscous damping dominates)

• Transitional Flow: 2,300 Re 4,000

• Turbulent Flow: Re > 4,000 (Chaotic eddies and high mixing)

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• Standard Fluid Dynamic Viscosity Benchmarks (@ 20°C)**:

• Liquid Water: 1.002 cP = 0.001002 Pa·s Re = 99,800 (Turbulent)

• SAE 10W-30 Motor Oil: 100.0 cP = 0.100 Pa·s Re = 875 (Laminar)

• SAE 50 Gear Oil: 500.0 cP = 0.500 Pa·s Re = 180 (Deep laminar)

• Pure Glycerin: 1,412.0 cP = 1.412 Pa·s

• Raw Honey: 10,000.0 cP = 10.000 Pa·s (10,000× more viscous than water)

How to Use This Calculator

Enter your Dynamic Viscosity Magnitude (µ / η) (e.g. 1.002 in viscosity), From Viscosity Unit — choose from Centipoise (cP = mPa·s - Universal Fluid Standard), Pascal-Seconds (Pa·s - SI Base Unit), Poise (P = 100 cP - CGS Unit), To Viscosity Unit — choose from Pascal-Seconds (Pa·s), Centipoise (cP = mPa·s), Poise (P), Flow Velocity (v in m/s for Reynolds Re) (e.g. 2.0 in m/s), Pipe Inside Diameter (D in mm) (e.g. 50 in mm), Fluid Density (ρ in kg/m³) (e.g. 1000 in kg/m³), and Rheological Fluid Benchmark — choose from Custom Dynamic Viscosity, Liquid Water @ 20°C (1.002 cP = 0.001002 Pa·s, ρ=1000) → Re = 99,800 (Highly Turbulent), SAE 10W-30 Motor Oil @ 20°C (100.0 cP, ρ=875) → 0.100 Pa·s | Re = 875 (Laminar Flow). Results update instantly as you type — adjust any value to compare scenarios.

The Formula

Reynolds Number: Re = (rho v D) / mu

Worked Example

A mechanical engineer pumping water at 2.0 m/s through a 50 mm pipe calculates Re = 99,800, confirming fully turbulent flow that requires a turbulent friction factor for pump head sizing.

Understanding Your Result

Unit conversions are exact by definition within a given measurement system (e.g., 1 km = exactly 1,000 m). Cross-system conversions (metric to imperial) use defined exchange factors: 1 inch = exactly 2.54 cm; 1 pound = 0.45359237 kg. Round your converted result to match the precision of your original measurement — expressing more decimal places than your input justifies implies false accuracy. For regulatory, legal, or safety-critical applications, verify which measurement system is required by the applicable standard.