This paper explores instances in Herodotus’ Histories where the historian or his characters engage with very large numbers by counting vast collections of people or things, establishing the dimensions of huge objects and measuring long stretches of time. In these episodes, Herodotus explores how quantifying the material traces of the past can help reconstruct antiquity. This methodological point is most evident in his calculations in book 2, and this paper focuses in particular on his persistent reckoning in three interrelated Egyptian accounts: those of the nature of the Nile valley, of the construction of the pyramids and of the genealogy of the Theban priests. I argue that Herodotus’ quantifying efforts, far from being only a rhetorical strategy to increase the narrator's credibility and authority, are an important, indeed crucial, part of his historical method.