Fluid Viscosity Calculator
Calculate dynamic and kinematic viscosity, Reynolds number, and viscosity conversions.
Find viscosity from temperature for water, air, and common fluids.
Convert between cP, mPa·s, cSt, and SSU.
Dynamic (Absolute) Viscosity η (mu) η = τ / (du/dy) Where τ = shear stress (Pa), du/dy = velocity gradient (1/s). SI unit: Pa·s (Pascal-second) = 1000 mPa·s = 1000 cP cP (centipoise): water at 20°C ≈ 1.002 cP — convenient reference point.
Kinematic Viscosity ν (nu) ν = η / ρ Where ρ = fluid density (kg/m³). SI unit: m²/s | Common unit: cSt (centistokes) = mm²/s Water at 20°C: ν ≈ 1.004 cSt (near 1 cSt — another convenient reference)
Viscosity Temperature Relationship Liquids: viscosity decreases strongly with temperature. Gases: viscosity increases with temperature (kinetic theory). Andrade equation for liquids: η = A × exp(B/T) where T is in Kelvin. For water (0–100°C): η ≈ 2.414×10⁻⁵ × 10^(247.8/(T−140)) Pa·s
Reynolds Number Re = ρVL/η = VL/ν Where V = velocity (m/s), L = characteristic length (pipe diameter, m). Re < 2300: laminar flow | Re 2300–4000: transition | Re > 4000: turbulent flow.
Common Unit Conversions 1 Pa·s = 1000 mPa·s = 1000 cP = 10 P (Poise) 1 m²/s = 10⁶ cSt = 10⁶ mm²/s SSU (Saybolt Universal Seconds): ν(cSt) ≈ 0.226×SSU − 195/SSU (for SSU 32–100)
Typical Viscosities (at ~20°C) Air: 0.018 cP | Water: 1.0 cP | Whole blood: 3–4 cP Olive oil: 80 cP | Motor oil SAE30: 90–110 cP | Honey: 2000–10000 cP Glycerol: 1412 cP | Tar pitch: 10⁸ cP