https://doi.org/10.1351/goldbook.12219
The equation for (z + 1)-average molar mass is \[M_{\rm{z+1}} = \frac{\sum\limits_{M} w_{M}M^{3}}{\sum\limits_M w_{M}M^{2}}\]
The equation for (z + 1)-average molecular weight is \[M_{\rm{r,z+1}} = \frac{\sum\limits_{M_{\rm{r}}} w_{M_{\rm{r}}}M^{3}}{\sum\limits_{M_{\rm{r}}} w_{M_{\rm{r}}}M^{2}}\]
Notes:
- For definition of the symbols, see molar-mass average.
- Quantities (z + 1)-average molecular weight, (z + 1)-average relative molar mass, and (z + 1)-average relative molecular mass (\(M_{\rm{r,z+1}}\)) are synonyms. These quantities are dimensionless (pure numbers) and are not associated with any units.