Absolute Viscosity: the force required to move a unit plane surface over another plane surface at unit velocity when surfaces are separated by a layer of fluid of unit thickness.
Unit of Absolute Viscosity in the metric system: poise and centipose
1 poise = 1 gram/(cm)(sec) and
1 centipoise = 1/100 poise
Unit of Absolute Viscosity in the English system: slugs/(ft)(sec)
1 slug/(ft)(sec) = 1/0.002089 poise
Kinematic Viscosity: the absolute viscosity divided by density.
Unit of Kinematic Viscosity in the metric system and commonly used in the countries using the
Other units of Kinematic Viscosity in the English system, the most practical unit for making
calculations is ft.2/sec.; 1 ft.2/sec. = 92903 centistoke and 1 centistoke = 1.0760 x 10-5 ft.2/sec.
Saybolt Universal Seconds, SSU, is the kinematic viscosity as determined by the time in seconds required for 60 cc of fluid to flow through a standard orifice.
Saybolt-Furol, SSF, utilizes a larger orifice and is used for very viscous fluids. Time of efflux is approx. 1/10 that of Universal.
Engler degrees are obtained by dividing the outflow time of a specified amount of fluid through a specified orifice by the outflow time of water at 68°F. The method is used predominantly in European countries.
Viscosity Index is an empirical number indicating the effect of temperature change on viscosity. Fluids with the same viscosity at a given temperature do not necessarily have the same viscosity index.
SAE Viscosity Numbers are a means of classifying crankcase lubricating oils in terms of viscosity. Other factors are not considered.