Poise (unit)

The poise (symbol P, /ˈpɔɪz/) is the unit of dynamic viscosity in the centimetre gram second system of units. It is named after Jean Louis Marie Poiseuille (and not related to the ordinary word poise, even though its meaning might seem connected).

$1\ {\mbox{P}}=1.00\ {\mbox{g}}\cdot {\mbox{cm}}^{-1}\cdot {\mbox{s}}^{-1}$

The analogous unit in the International System of Units is the pascal second (Pa·s):

$1\ {\mbox{Pa}}\cdot {\mbox{s}}=1\ {\mbox{kg}}\cdot {\mbox{m}}^{-1}\cdot {\mbox{s}}^{-1}=10\ {\mbox{P}}$

The poise is often used with the metric prefix centi-. A centipoise is one one-hundredth of a poise, and one millipascal-second (mPa·s) in SI units. (1 cP = 10⁻² P = 10⁻³ Pa·s = 1 mPa·s)

Centipoise is properly abbreviated cP, but the alternative abbreviations cps, cp, and cPs are also commonly seen.

Water has a viscosity of 0.00899 Poise at 25 °C and a pressure of 1 atmosphere. (0.00899 P = 0.899cP = 0.899 mPa·s)

Use in laboratory

A viscometer can be used to measure centipoise.

When determining centipoise, all other fluids are calibrated to the viscosity of distilled water at STP. (in some practices, one can use the following approximation: water at approximately 70 °F (21 °C) is about one centipoise).

Thicker liquids, like honey, have higher viscosities. For example, while ethylene glycol has a viscosity of just 24 centipoise at 23 C, honey has a viscosity of 2 000 centipoise and molasses has a viscosity of 5 000 centipoise. Lard has a viscosity of 100 000 centipoise.

See also

• Viscosity