Molar mass ($M,M_n$)

Molar mass is mass per amount of substance, commonly expressed in $\mathrm{g}\mathrm{mo}{\mathrm{l}}^{-1}$. For chain counts $n_i$ and chain molar masses $M_i$, the number average is $M_n={\sum }_i{n}_i{M}_i/{\sum }_i{n}_i$. Relating it to a degree of polymerization requires a defined unit-mass convention and end-group accounting.