Kinematic and Dynamic Viscosity Converter
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 page converts in both directions: dynamic to kinematic with ν = μ/ρ, and kinematic back to dynamic with μ = ν × ρ. Results in m²/s, centistokes, Pa·s, and centipoise.
Calculate kinematic viscosity (ν = μ/ρ)
Results
Convert kinematic to dynamic viscosity (μ = ν × ρ)
The reverse conversion. Use this when a datasheet quotes kinematic viscosity in centistokes (common for lubricating oils, where ISO VG grades are defined in cSt at 40 °C) and you need dynamic viscosity in Pa·s or centipoise.
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 accounts for 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, which is why cSt gives clean numbers for everyday fluids.
Related tools
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Kinematic vs dynamic viscosity
A plain-English guide to viscosity: what it means and when each form is used.
How to read the Moody Chart
What to do with Reynolds number once you have it: reading friction factor off the chart.
Colebrook-White vs Swamee-Jain
Two ways to get friction factor from Re and ε/D, and when each is accurate enough.