Dynamic viscosity, also known as absolute viscosity, measures a fluid's internal resistance to flow when subjected to an external shear stress. In engineering, converting between the Imperial system and the International System of Units (SI) is a frequent requirement for fluid mechanics calculations.
Pound per foot-second (lb/(ft·s)): This is a unit of dynamic viscosity in the English Engineering system. It represents the force in pounds-force required to move a surface of one square foot at a velocity of one foot per second relative to a parallel surface separated by one foot of fluid.
Pascal-second (Pa·s): The SI derived unit for dynamic viscosity. One Pascal-second is equivalent to one Newton-second per square meter (N·s/m²).
The conversion factor is derived from the fundamental definitions of force, mass, and length. Specifically, \(1 \text{ lb/(ft·s)} \approx 1.488164 \text{ Pa·s}\). This conversion is essential when transitioning from legacy technical specifications to modern standardized design protocols.
Pound per foot-second to Pascal-second Conversion Reference Table
Pound per foot-second (lb/(ft·s))
Pascal-second (Pa·s)
0.1
0.1488
0.5
0.7441
1.0
1.4882
2.0
2.9763
5.0
7.4408
10.0
14.8816
20.0
29.7633
50.0
74.4082
100.0
148.8164
500.0
744.082
1000.0
1488.164
Conversion Example
To convert a dynamic viscosity value from lb/(ft·s) to Pa·s, multiply the given value by the conversion factor of 1.488164.
The factor 1.488164 is derived from the conversion of pounds-force to Newtons and feet to meters. Since 1 lbf is approximately 4.44822 N and 1 ft is 0.3048 m, the ratio of these units results in the specific constant used for dynamic viscosity.
No, they are different. While both measure dynamic viscosity, centipoise (cP) is a CGS unit where 1 cP = 0.001 Pa·s. To convert lb/(ft·s) to centipoise, you would multiply by 1488.164.
"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)