It is easier to use a single value to compare different polymers with each other.
Therefore, for the viscosity commonly the MVR (melt volume-flow rate) is used.
This value describes how much mass of a polymer is flowing during 10 minutes at a specific temperature and pressure (mostly 2,16 kg or 5 kg) through a given capillary.
The measurement of the volume can be done directly during the experiment, therefore no additional step is necessary.
The higher the MVR, the smaller the viscosity of the polymer.
The used unit is cm^3/ 10 min.