  The effective on-site Coulomb interaction (Hubbard $U$) between localized
\textit{d} electrons in 3\textit{d}, 4\textit{d}, and 5\textit{d} transition
metals is calculated employing a new parameter-free realization of the
constrained random-phase approximation using Wannier functions within the
full-potential linearized augmented-plane-wave method. The $U$ values lie
between 1.5 and 5.7 eV and depend on the crystal structure, spin polarization,
\textit{d} electron number, and \textit{d} orbital filling. On the basis of the
calculated $U$ parameters, we discuss the strength of the electronic
correlations and the instability of the paramagnetic state towards the
ferromagnetic one for 3\textit{d} metals.
