Kinematic Viscosity Calculator
The Reynolds Number Calculator requires kinematic viscosity (ν) as an input - but many fluid data tables list dynamic viscosity (μ) and density (ρ) separately. This calculator converts them instantly: ν = μ/ρ. Results in m²/s and centistokes (cSt).
Calculate Kinematic Viscosity (ν = μ/ρ)
Results
Dynamic vs Kinematic Viscosity - What's the Difference?
Both describe how "thick" or "syrupy" a fluid is - but they measure slightly different things.
Dynamic viscosity (μ) - sometimes called absolute viscosity - is the fluid's resistance to shear stress. Think of it as the force needed to slide one layer of fluid past another. Units: Pa·s (Pascal-seconds), or the older unit mPa·s (millipascal-seconds), where 1 mPa·s = 1 cP (centipoise).
Kinematic viscosity (ν) is dynamic viscosity divided by density. It accounts for the fact that denser fluids have more inertia - and inertia affects how easily flow becomes turbulent. It's what appears in the Reynolds number formula Re = VD/ν. Units: m²/s, or the convenient unit cSt (centistoke), where 1 cSt = 10⁻⁶ m²/s.
The Formula
ν = μ / ρ - ν - kinematic viscosity (m²/s)
- μ - dynamic viscosity (Pa·s)
- ρ - fluid density (kg/m³)
Reference Values for Common Fluids
Frequently Asked Questions
How does temperature affect kinematic viscosity?
For liquids, kinematic viscosity decreases with temperature - hot water is less viscous than cold water. For gases, the opposite is true: kinematic viscosity increases with temperature because gas density decreases faster than dynamic viscosity increases. This matters when designing systems that operate across a temperature range.
Why does the Reynolds number use kinematic rather than dynamic viscosity?
The Reynolds number Re = VD/ν already "bakes in" density. If you use dynamic viscosity instead, you need to include density explicitly: Re = ρVD/μ. Both formulas give the same result - kinematic viscosity just makes the formula more compact. Use whichever form matches your data.
What is 1 centistoke in m²/s?
1 cSt = 1 mm²/s = 1 × 10⁻⁶ m²/s. Water at 20°C ≈ 1 cSt. This is why cSt is a convenient unit - it gives clean numbers for everyday fluids.