We prove that the set of singular vectors in R d , d ≥ 2, has Hausdorff dimension d 2 d+1 and that the Hausdorff dimension of the set of ε-Dirichlet improvable vectors in R d is roughly d 2 d+1 plus a power of ε between d 2 and d. As a corollary, the set of divergent trajectories of the flow by diag(e t , . . . , e t , e −dt ) acting on SL d+1 (R)/ SL d+1 (Z) has Hausdorff codimension d d+1 . These results extend the work of the first author in [6].