Fluid Viscosity Calculator
Calculate dynamic and kinematic viscosity and Reynolds number for common fluids.
Convert between cP, mPa·s, cSt, and SSU with temperature data for water.
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