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Convert dynamic viscosity from poise (P) to pascal-seconds (Pa·s) with precision
Pa·s = P ÷ 10
P = Pa·s × 10
| Poise (P) | Pascal-seconds (Pa·s) |
|---|---|
| 0.01 | 0.001 |
| 0.1 | 0.01 |
| 0.5 | 0.05 |
| 1 | 0.1 |
| 2 | 0.2 |
| 5 | 0.5 |
| 10 | 1 |
| 20 | 2 |
| 50 | 5 |
| 100 | 10 |
| 500 | 50 |
| 1,000 | 100 |
The poise (P) is the CGS unit of dynamic viscosity, named after French physicist Jean Léonard Marie Poiseuille. One poise is defined as one dyne-second per square centimeter (dyn·s/cm²). The poise was historically significant in fluid mechanics research and industrial applications. However, it has largely been replaced by its subdivision, the centipoise (1 P = 100 cP), which provides more convenient values for common fluids. The poise is still encountered in older technical literature and some specialized applications. Water at 20°C has a viscosity of approximately 0.01 poise, or 1 centipoise, making the smaller unit more practical for everyday use.
The pascal-second (Pa·s) is the SI unit of dynamic viscosity, representing the force per unit area required to maintain unit velocity gradient in a fluid. One pascal-second equals one newton-second per square meter (N·s/m²) or one kilogram per meter per second (kg/(m·s)). The pascal-second provides a consistent, internationally recognized standard for viscosity measurements in scientific research, engineering calculations, and technical specifications. Its relationship to fundamental SI units makes it ideal for theoretical work and computational modeling. While the values may be small for common fluids (water is 0.001 Pa·s), the unit is essential for maintaining dimensional consistency in complex equations.
The transition from poise to pascal-seconds reflects the broader shift from the CGS (centimeter-gram-second) system to the SI (International System of Units). The poise was established in the early 20th century and became standard in fluid mechanics research. However, as international scientific cooperation grew, the need for a unified measurement system became apparent.
The SI system, adopted globally in the 1960s, uses meters, kilograms, and seconds as base units. This makes the pascal-second the natural choice for viscosity. Despite this official change, the centipoise (0.01 poise) remains popular in industry because 1 cP equals the viscosity of water, providing an intuitive reference point. Many modern industries use both systems: centipoise for practical measurements and pascal-seconds for formal documentation and scientific publications.
Start with the dynamic viscosity measurement in poise (P).
Divide the poise value by 10 to convert to pascal-seconds. The formula is: Pa·s = P ÷ 10.
Perform the division to obtain the viscosity in pascal-seconds. For example: 5 P ÷ 10 = 0.5 Pa·s.
Check that the pascal-seconds value is smaller than the poise value, as 1 Pa·s = 10 P.
Glycerin with viscosity of 15 poise:
15 P ÷ 10 = 1.5 Pa·s
Converting historical viscosity data from older publications using poise to modern SI units for comparative studies.
Harmonizing viscosity specifications across different countries and industries that use varying unit systems.
Translating material safety data sheets and product specifications between CGS and SI unit systems.
Designing and optimizing processes involving polymers, resins, and other high-viscosity materials.
Investigating the flow behavior of complex fluids, non-Newtonian fluids, and viscoelastic materials.
Ensuring consistency in manufacturing processes where viscosity is a critical quality parameter.
| Material | Viscosity (P) | Viscosity (Pa·s) |
|---|---|---|
| Air (20°C) | 0.00018 | 0.000018 |
| Water (20°C) | 0.01 | 0.001 |
| Ethanol | 0.012 | 0.0012 |
| Mercury | 0.015 | 0.0015 |
| Motor Oil SAE 10 | 0.65 | 0.065 |
| Motor Oil SAE 30 | 2-3 | 0.2-0.3 |
| Olive Oil | 0.8-1 | 0.08-0.1 |
| Castor Oil | 6-10 | 0.6-1 |
| Glycerin | 15 | 1.5 |
| Honey | 20-100 | 2-10 |
One poise equals 0.1 pascal-seconds. Conversely, one pascal-second equals 10 poise. This conversion factor arises from the difference between CGS and SI base units.
1 poise (P) = 100 centipoise (cP) = 0.1 pascal-seconds (Pa·s). Therefore, 1 cP = 0.001 Pa·s. The centipoise is the most commonly used unit in practice because it provides convenient values for most liquids.
The unit honors Jean Léonard Marie Poiseuille, a 19th-century French physicist and physician who studied blood flow and derived the Hagen-Poiseuille equation describing laminar flow through cylindrical pipes. His work was fundamental to understanding viscosity's role in fluid dynamics.
The poise itself is rarely used in modern applications. However, its subdivision—the centipoise—remains extremely popular in industries like petroleum, pharmaceuticals, and food processing. For formal scientific work, pascal-seconds are preferred as the SI standard.
A Newtonian fluid has constant viscosity regardless of applied shear stress or shear rate. Water, air, and most simple liquids are Newtonian. Non-Newtonian fluids like ketchup, blood, or paint have viscosity that changes with shear conditions, making their characterization more complex.
Required accuracy depends on the application. Quality control in pharmaceuticals may need ±1% precision, while rough process estimates might tolerate ±10%. Temperature control is critical because viscosity can change 2-5% per degree Celsius for many liquids.
Air at 20°C has a viscosity of about 0.00018 poise (0.018 cP), while water is 0.01 poise (1 cP)—roughly 55 times more viscous. Despite being a gas, air still exhibits viscosity, which is crucial in aerodynamics and weather systems.