Summary: We investigate hardness of one-way functions (i.e., difficulty of computing inverse of one-way functions). Here, the notion of polynomial lowness [{\it U. Schöning}, J. Comput. Syst. Sci. 27, 14-28 (1983; Zbl 0515.68046)] is used to measure the difficulty of a given problem. We show that, for any one-way function f, the hardness of f is similar to the complexity of dom(f) and rang(f).