# Poise (unit)

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.

poise
Unit systemCentimetre–gram–second system of units
Unit ofDynamic viscosity
SymbolP
Named afterJean Léonard Marie Poiseuille
Derivation1 P = 1 dyn⋅s/cm2
Conversions
1 P in ...... is equal to ...
CGS base units   1 cm−1⋅g⋅s−1
SI units   0.1 Pa⋅s

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]

## References

1. ^ Gooch, Jan W. (2010). Encyclopedia dictionary of polymers (2nd ed.). Berlin: Springer. ISBN 978-1-4419-6246-1.
2. ^ Reid, Robert C. (1987). The Properties of Gases and Liquids (4th ed.). McGraw-Hill.
3. ^ Parker, Sybil P. (1988). Fluid Mechanics Source Book (1st ed.). McGraw-Hill.
4. ^ Lide, David R. (1994). CRC Handbook of Thermophysical and Thermochemical Data (1st ed.). CRC Press.
5. ^ "Viscosity of Liquids", in CRC Handbook of Chemistry and Physics, 91st Edition, W.M. Haynes, ed., CRC Press/Taylor and Francis, Boca Raton, Florida, 2010-2011.