By definition,
:1 reyn = 1 lb s in.
It follows that the relation between the reyn and the poise is approximately
:1 reyn = 6.89476 × 10 P.
In SI units, viscosity is expressed in newton-seconds per square meter, or equivalently in pascal-seconds. The conversion factor between the two is approximately
:1 reyn = 6890 Pa s.