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poise

The unit of absolute, or dynamic, viscosity in the centimeter-gram-second system of units. Symbol, P, though some say Po.¹ The poise is the most commonly encountered unit of viscosity, often as the centipoise.

One poise is the viscosity of a fluid that requires a shearing force of 1 dyne to move a square centimeter area of either of two parallel layers of fluid 1 centimeter apart with a velocity of 1 centimeter per second relative to the other layer, the space between the layers being filled with the fluid. One poise = 0.1 pascal-second = 0.1 poiseuille.

This unit was defined around 1924, and named for Jean Louis Marie Poiseuille (1779–1869). Its pronunciation reflects its French origin: not like the poise in “she showed great poise,” but pwäz.

According to the current national standard in the United States², the poise is not to be used. The pascal-second should be used instead.

1. P according to the International Union of Pure and Applied Physics Document U.I.P. 11 (S.U.N. 65-3).

2. IEEE/ASTM SI 10™-2002.
American National Standard for Use of the International System of Units (SI): The Modern Metric System.
New York: IEEE, 30 December 2002.

See Section 3.3.3.