Statistical segment length ($b^2=⟨R^2⟩/N$)

An effective step length describing a specified chain-count convention: an ideal polymer with $N$ counted units has mean-squared end-to-end distance of a polymer chain $⟨R^2⟩=N{b}^2$. If $N$ counts freely jointed coarse-grained units, $b$ is their Kuhn length. If $N$ counts chemical repeat units, the effective $b$ incorporates local conformational correlations and is not automatically a physical monomer diameter. A repeat-unit volume $v_0$ is independent information; setting $v_0\sim b^3$ is a scaling approximation.