 Molar-mass dispersity

The weight-average molar mass divided by the number-average molar mass. Its conventional written symbol is Đ. With number weighting it equals $1+\mathrm{Var}(M)/⟨M{⟩}^2$, so it is at least one and equals one only for a uniform molar mass. It measures one aspect of distribution breadth, not the full shape of a molar mass distribution.