(for the simplest case of linear polymers formed from two monomers in equimolar quantities) as per Carothers' equation:

where is the molecular mass of the repeating unit.

Z-average molar mass

The z-average molar mass is the third moment or third power average molar mass, which is calculated by

The z-average molar mass can be determined with ultracentrifugation. The melt elasticity of a polymer is dependent on .