In the present paper, we propose and supply evidence for the following conjecture, aimed at characterizing uniform pro-p groups. Suppose that pa parts per thousand yen3 and let G be a torsion-free pro-p group of finite rank. Then G is uniform if and only if its minimal number of generators is equal to the dimension of G as a p-adic manifold, i.e. d(G) = dim(G). In particular, we prove that the assertion is true whenever G is soluble or p > dim(G).