Water Dynamic (Absolute) and Kinematic Viscosity Calculator

Dynamic (absolute) viscosity (μ) measures a fluid's resistance to shear flow. It is measured in mPa·s (millipascal-seconds), equivalent to cP (centipoise). Newton's law of viscosity is:

τ = μ × (du / dy)

where τ is shear stress and du/dy is the velocity gradient perpendicular to flow.

Water viscosity decreases significantly with increasing temperature — by nearly a factor of 30 from 32°F to 675°F. This affects pressure drop, pump power requirements, and flow regime. The Reynolds number determines whether flow is laminar or turbulent:

Re = ρ × v × D / μ

At low temperatures, higher viscosity can push systems toward laminar flow (Re < 2300) where heat transfer efficiency drops sharply. At elevated temperatures and pressures (above 212°F), water remains liquid only under pressure — the saturation pressure values in the data table reflect this condition.

Dynamic viscosity (also called absolute viscosity or static viscosity) measures a fluid's resistance to shear — the internal force per unit area required to make one layer of fluid slide past another. It is independent of density. The SI unit is the pascal-second (Pa·s); the common engineering unit is the millipascal-second (mPa·s), numerically equal to centipoise (cP).

τ = μ × (du / dy)

where τ is shear stress [Pa] and du/dy is the velocity gradient [s⁻¹].

Kinematic viscosity is the ratio of dynamic viscosity to fluid density. It describes how easily a fluid flows under the influence of gravity or pressure, without needing to separately account for the applied force. The SI unit is m²/s; the common unit is mm²/s, numerically equal to centistokes (cSt).

ν = μ / ρ

Kinematic viscosity is derived from dynamic viscosity and density:

ν [cSt] = μ [mPa·s] × 1000 / ρ [kg/m³]

Because water has a density very close to 1000 kg/m³ near room temperature, its kinematic viscosity in cSt is numerically very close to its dynamic viscosity in cP. At elevated temperatures, water density decreases, so kinematic viscosity diverges slightly above the cP value.

Use dynamic (absolute) viscosity for: pump power calculations, pipe pressure drop (Darcy–Weisbach), Reynolds number (Re = ρvD/μ), and any situation where force or stress is the driving input.

Use kinematic viscosity for: gravity-driven flow, lubrication ratings, most viscometer measurements, and flow calculations where density is already embedded in the formula (e.g., Stokes' law, ASTM oil viscosity grades).

Note: "Absolute viscosity" and "static viscosity" are synonyms for dynamic viscosity — they all refer to the same physical property. "Static" distinguishes it from apparent viscosity measured at elevated shear rates in non-Newtonian fluids.

Units: centipoise (cP), poise (P), pascal-second (Pa·s), pound/(foot second) (lb/(ft·s)), pound/(foot hour) (lb/(ft·h))

• 1 cP = 0.001 Pa·s = 0.01 P = 6.72197×10⁻⁴ lb/(ft·s) = 2.4191 lb/(ft·h)
• 1 lb/(ft·h) = 2.7778×10⁻⁴ lb/(ft·s) = 4.1338×10⁻⁴ Pa·s = 0.41338 cP
• 1 lb/(ft·s) = 3600 lb/(ft·h) = 1.48816 Pa·s = 1488.16 cP
• 1 Pa·s = 1 kg/(m·s) = 1 (N·s)/m² = 10 P = 1000 cP = 0.672197 lb/(ft·s) = 2419.08 lb/(ft·h)
• 1 P = 1 g/(cm·s) = 0.1 Pa·s = 100 cP = 0.067197 lb/(ft·s) = 241.909 lb/(ft·h)
• 1 Pa·s = 0.00014504 reyn; 1 reyn = 6894.76 Pa·s

Units: centistoke (cSt), stoke (St), ft²/s, ft²/h, in²/s, m²/s

• 1 cSt = 1 mm²/s = 10⁻⁶ m²/s = 1.07639×10⁻⁵ ft²/s = 0.03875 ft²/h = 1.55×10⁻³ in²/s
• 1 St = 1 cm²/s = 100 cSt = 10⁻⁴ m²/s = 1.076×10⁻³ ft²/s = 3.875 ft²/h
• 1 ft²/s = 92903 cSt = 929.03 St = 0.09290 m²/s = 3600 ft²/h = 144 in²/s
• 1 ft²/h = 2.7778×10⁻⁴ ft²/s = 25.806 cSt = 0.25806 St
• 1 in²/s = 6.944×10⁻³ ft²/s = 645.16 cSt = 6.4516 St
• 1 m²/s = 10⁶ cSt = 10⁴ St = 10.764 ft²/s = 1550 in²/s