Poise (unit)

Poise (symbol: P) is the unit of dynamic viscosity (also known as absolute viscosity) in the centimetre-gram-second (CGS) system of units. It is named after French physicist Jean Léonard Marie Poiseuille.

One poise is defined as the viscosity of a fluid in which a force of 1 dyne per square centimeter is required to maintain a velocity gradient of 1 centimeter per second. This can also be expressed as 1 g⋅cm−1⋅s−1 or 0.1 Pa⋅s (Pascal-seconds) in SI units.

Because the poise is a relatively large unit, the centipoise (cP), which is one hundredth of a poise (0.01 P), is more commonly used. Water at 20 °C has a viscosity of approximately 1 cP. The viscosity of air is much lower, around 0.018 cP at room temperature.

Conversion factors:

• 1 P = 0.1 Pa⋅s
• 1 cP = 0.001 Pa⋅s
• 1 P = 1 g⋅cm−1⋅s−1
• 1 cP = 1 mPa⋅s (millipascal-seconds)

While the poise is still encountered, particularly in older scientific literature, the SI unit of viscosity, the pascal-second (Pa⋅s), is the preferred unit in modern scientific and technical contexts.