The poise (symbol P; /pɔɪz, pwɑːz/) is the unit of dynamic viscosity (absolute viscosity) in the centimetre–gram–second system of units (CGS).^[1] It is named after Jean Léonard Marie Poiseuille (see Hagen–Poiseuille equation). The centipoise (1 cP = 0.01 P) is more commonly used than the poise itself.

Dynamic viscosity has dimensions of ${\displaystyle \mathrm {force\times time/area} }$, that is, ${\displaystyle [{\mathsf {M))^{1}{\mathsf {L))^{-1}{\mathsf {T))^{-1}]}$.

$${\displaystyle 1~{\text{P))=0.1~{\text{m))^{-1}{\cdot }{\text{kg)){\cdot }{\text{s))^{-1}=1~{\text{cm))^{-1}{\cdot }{\text{g)){\cdot }{\text{s))^{-1}=1~{\text{dyn)){\cdot }{\text{s)){\cdot }{\text{cm))^{-2}.}$$

The analogous unit in the International System of Units is the pascal-second (Pa⋅s):^[2]

$${\displaystyle 1~{\text{Pa)){\cdot }{\text{s))=1~{\text{N)){\cdot }{\text{s)){\cdot }{\text{m))^{-2}=1~{\text{m))^{-1}{\cdot }{\text{kg)){\cdot }{\text{s))^{-1}=10~{\text{P)).}$$

The poise is often used with the metric prefix centi- because the viscosity of water at 20 °C (standard conditions for temperature and pressure) is almost exactly 1 centipoise.^[3] A centipoise is one hundredth of a poise, or one millipascal-second (mPa⋅s) in SI units (1 cP = 10⁻³ Pa⋅s = 1 mPa⋅s).^[4]

The CGS symbol for the centipoise is cP. The abbreviations cps, cp, and cPs are sometimes seen.

Liquid water has a viscosity of 0.00890 P at 25 °C at a pressure of 1 atmosphere (0.00890 P = 0.890 cP = 0.890 mPa⋅s).^[5]