Dynamic viscosity, also known as absolute viscosity, measures a fluid's internal resistance to flow when subjected to an external shear stress. In engineering, two primary units are frequently encountered: the Pascal-second (Pa·s) and the Poise (P).
Pascal-second (Pa·s): The SI derived unit of dynamic viscosity. It is defined as \(1 \text{ Pa} \cdot \text{s} = 1 \text{ N} \cdot \text{s} / \text{m}^2\). It is the standard unit used in modern scientific and industrial calculations.
Poise (P): A CGS (centimeter-gram-second) unit named after Jean Léonard Marie Poiseuille. While technically deprecated in favor of SI units, it remains prevalent in the petroleum and chemical industries, often expressed as centipoise (cP), where \(1 \text{ cP} = 0.01 \text{ P}\).
The relationship between these units is defined by the factor of 10, as \(1 \text{ Pa} \cdot \text{s} = 10 \text{ P}\). Understanding this conversion is critical for fluid mechanics, lubrication engineering, and polymer processing.
Pascal-second to Poise Conversion Reference Table
Pascal-second (Pa·s)
Poise (P)
0.1
1
0.5
5
1.0
10
2.0
20
5.0
50
10.0
100
20.0
200
50.0
500
100.0
1000
500.0
5000
1000.0
10000
Conversion Example
To convert a dynamic viscosity value from Pascal-seconds to Poise, multiply the value by 10. For instance, if you have a fluid with a viscosity of 10 Pa·s:
The Poise remains in use primarily due to legacy industrial standards and the convenience of the centipoise (cP) scale. Water at 20°C has a viscosity of approximately 1 cP, making it a very intuitive reference point for many chemical engineers.
Since 1 Pa·s equals 1000 centipoise (cP), you simply divide your cP value by 1000 to obtain the result in Pa·s. For example, 500 cP is equal to 0.5 Pa·s.
"On fait la science avec des faits, comme on fait une maison avec des pierres ; mais une accumulation de faits n'est pas plus une science qu'un tas de pierres n'est une maison." "Science is built up of facts, as a house is built of stones; but an accumulation of facts is no more a science than a heap of stones is a house." — Henri Poincaré (French Mathematician, Theoretical Physicist & Mining Engineer)