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 Poise (P) and the Pascal-second (Pa·s).
The Poise (P) is a CGS (centimeter-gram-second) unit named after Jean Léonard Marie Poiseuille. While historically significant, it is often expressed in practice as centipoise (cP) because 1 P is relatively high for common fluids like water. The Pascal-second (Pa·s) is the SI (International System of Units) derived unit, defined as the viscosity of a fluid in which a stress of one pascal produces a velocity gradient of one meter per second per meter.
Poise (P): Commonly used in the petroleum and chemical industries, often in the form of cP. \(1 \text{ P} = 0.1 \text{ Pa} \cdot \text{s}\).
Pascal-second (Pa·s): The standard unit in modern engineering calculations and fluid dynamics modeling. \(1 \text{ Pa} \cdot \text{s} = 10 \text{ P}\).
Poise to Pascal-second Conversion Reference Table
Poise (P)
Pascal-second (Pa·s)
0.1
0.01
0.5
0.05
1.0
0.1
2.0
0.2
5.0
0.5
10.0
1
20.0
2
50.0
5
100.0
10
500.0
50
1000.0
100
Conversion Example: 10 Poise to Pascal-seconds
To convert dynamic viscosity from Poise (P) to Pascal-seconds (Pa·s), multiply the value by the conversion factor of 0.1.
The Poise is a relatively large unit for many common fluids. For instance, water at 20°C has a viscosity of approximately 1 cP (0.01 P). Using centipoise allows engineers to work with more manageable whole numbers.
No, they are not equivalent. One Pascal-second is exactly ten times larger than one Poise. Always ensure you are using the correct SI conversion factor of 0.1 when moving from CGS to SI units.
"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)