About

Fluid mechanics requires precise distinction between dynamic and kinematic viscosity. Dynamic viscosity measures internal resistance to flow, while kinematic viscosity accounts for the fluid's density under gravity. Engineers calculating Reynolds numbers or sizing pumps often receive lab data in Centipoise (cP) but require Centistokes (cSt) for hydraulic equations.

This conversion relies heavily on the specific gravity or density of the medium. A minor deviation in density input significantly alters the kinematic output, potentially leading to errors in head loss estimation or lubrication film thickness. This tool integrates a density variable directly into the calculation workflow, ensuring adherence to the physical relationship between stress, deformation, and mass.

Formulas

The relationship between kinematic viscosity, dynamic viscosity, and density is defined by the ratio:

ν = μρ

Where:

ν (Nu) = Kinematic Viscosity m²/s
μ (Mu) = Dynamic Viscosity Pa⋅s
ρ (Rho) = Density kg/m³

Reference Data

Fluid (approx 20°C)	Density kg/m³	Dynamic cP	Kinematic cSt
Water	998.2	1.002	1.004
Mercury	13534	1.526	0.113
Ethanol	789	1.20	1.52
SAE 10 Oil	870	100	115
SAE 30 Oil	890	250	280
Glycerin	1261	1412	1120
Olive Oil	918	84	91.5
Honey	1420	10000	7042
Air (Sea Level)	1.225	0.018	14.8

Frequently Asked Questions

Kinematic viscosity represents the ratio of viscous force to inertial force. Since inertia is a function of mass (density), you cannot convert the absolute stickiness (dynamic viscosity) to its flow behavior under gravity (kinematic) without knowing the fluid's mass per unit volume.

Centipoise (cP) is a unit of Dynamic Viscosity, measuring absolute resistance. Centistokes (cSt) is a unit of Kinematic Viscosity, measuring flow diffusivity. Water at 20°C is the reference point for both, effectively 1 cP and 1 cSt.

Viscosity is highly temperature-dependent. Liquids generally become less viscous as temperature rises, while gases become more viscous. The densities provided in the tool are approximations at Standard Temperature (20°C). For high-precision engineering, use the density value specific to your operating temperature.