Quantities and Units of Viscosity

Dynamic viscosity is the ratio of the shearing stress to rate of deformation according to Newton's law of viscosity. The SI unit of dynamic voscosity is pascal second (Pa·s).

Kinematic viscosity is the ratio of dynamic viscosity to density of the fluid.The SI unit of the quantity is square meter per second (symbol m²/s).

Dynamic viscosity and kinematic viscosity can be calculated by each other here.

The Saybolt Universal Viscosity (abbr. SUV) can be converted to KV, and vice versa. The Saybolt Universal Viscosity is obtained under specified testing method - ASTM D 88. The corrected efflux time in seconds of 60 mL of sample flowing through a calibrated Universal orifice under specified conditions. The viscosity value is reported in Saybolt Universal seconds, abbreviated SUS, at a specified temperature.

Viscosity Index (VI) is a dimensionless quantity to evalulate the extent of how viscosity changes with the change of temperature. The larger the viscosity index, the more stable the viscosity with the change of temperature. It can be calculated under specified method.

KV-T property of a petroleum fluid descripts how kinematic viscosity changes with the change of its temperature.The kinematic viscosity of a petroleum oil or liquid hydrocarbon at any temperature within a limited range can be ascertained, provided that the kinematic viscosities at two temperatures are known.

Engine Oil Viscosity Classifications