Dimensions of Zassenhaus filtration subquotients of some pro-p-groups

We compute the ${\mathbb F}_p$-dimension of an $n$-th graded piece $G_{(n)}/G_{(n+1)}$ of the Zassenhaus filtration for various finitely generated pro-$p$-groups $G$. These groups include finitely generated free pro-$p$-groups, Demushkin pro-$p$-groups and their free pro-$p$ products. We provide a unifying principle for deriving these dimensions.