We propose a new measure to characterize the dimension of complex networks based on the ergodic theory of dynamical systems. This measure is derived from the correlation sum of a trajectory generated by a random walker navigating the network, and extends the classical Grassberger-Procaccia algorithm to the context of complex networks. The method is validated with reliable results for both synthetic networks and real-world networks such as the world air-transportation network or urban networks, and provides a computationally fast way for estimating the dimensionality of networks which only relies on the local information provided by the walkers. Preprint version merging the main article and the supplementary material. To be published in Physical Review Letters.PACS numbers: 05.45. Ac,89.75.Fb Network science has influenced the recent progress in many areas of statistical and nonlinear physics [1]. The discovery of the real architecture of interactions of many systems studied under the former disciplines [2-4] changed the usual mean-field way to tackle problems arising in sociology, biology, epidemiology and technology among others [5]. Furthermore, the blossom of the network theoretical machinery [6], has provided a forefront framework to interpret the relations encoded in large datasets of diverse nature and fostered the application of new techniques, such as community detection algorithms [7], to coarse-grain the complex and hierarchical landscape of interactions of real-world systems.Recently, geometrical concepts have been exploited to describe and classify the structure of complex networks beyond purely topological aspects [8][9][10][11]. In particular, the box-counting technique, widely used for estimating the capacity dimension D 0 of an object, has been recently extended, as a box-covering algorithm, to characterize the dimensionality of complex networks [11][12][13][14]. This technique proceeds by calculating the number N of boxes of Euclidean volume L d required to cover an object, being the capacity dimension D 0 of such object given by D 0 = lim L→0 log N log(1/L) . The capacity dimension D 0 is thus seen as an upper bound to the Hausdorff dimension.The box-covering approach, while being the most natural and elegant extension of the concept of fractal dimension to networks, suffers from some difficulties. First, in order to tile the network and to unambiguosly relate the box-covering and capacity dimensions, the object under study must be embedded in a metric space, something that does not apply in the more general case of a complex network. This subtle problem can be overcome by restricting to spatially embedded complex networks [14]. A second important issue is the need of full knowledge of the network topology in order to perform the box-covering procedure. This constraint faces the limitations related to storing the complete network backbone, indeed, the computation of the capacity dimension becomes unpractical for embedding dimensions larger than 3 [15]. Finally, another related problem is tha...