Dynamic viscosity, or absolute viscosity, measures a fluid's internal resistance to flow under an applied shear stress. In engineering, converting between the Imperial system and the metric CGS (centimeter-gram-second) system is a frequent requirement for fluid mechanics calculations.
Pound per foot-second (lb/(ft·s)): This is the English Engineering unit for dynamic viscosity. It represents the force in pounds-force required to move a plane surface of one square foot at a velocity of one foot per second relative to another plane surface, separated by a fluid film of one foot thickness.
Centipoise (cP): A common metric unit derived from the Poise (P), where \(1 \text{ cP} = 0.01 \text{ P}\). It is widely used in industrial applications, such as characterizing the viscosity of oils, paints, and chemical reagents.
The conversion factor is derived from the relationship between the pound-mass, foot, and second to the gram, centimeter, and second. Specifically, \(1 \text{ lb/(ft·s)} \approx 1488.164 \text{ cP}\).
Pound per foot-second to Centipoise Conversion Reference Table
Pound per foot-second (lb/(ft·s))
Centipoise (cP)
0.1
148.8164
0.5
744.082
1.0
1488.164
2.0
2976.328
5.0
7440.82
10.0
14881.64
20.0
29763.28
50.0
74408.2
100.0
148816.4
500.0
744082
1000.0
1.4882e+06
Conversion Example
To convert a dynamic viscosity value from lb/(ft·s) to cP, multiply the given value by the conversion factor of 1488.164.
Centipoise is preferred because water at 20°C has a viscosity of approximately 1 cP. This provides a convenient, intuitive reference point for engineers when comparing the flow characteristics of various industrial fluids.
The factor 1488.164 is a high-precision approximation based on the standard gravitational acceleration and the definition of the pound-mass. For most engineering applications, this precision is sufficient, though it should be rounded based on the significant figures of your input data.
"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)