It’s normal and natural to think that how much we know, individually and collectively, grows over time. What could seem more obvious and unremarkable than the claim that, for example, I know more now than I did when I was 10 years old? Or that I know more now about Edinburgh than I did when I first moved here five years ago? Yet when we think carefully about what it is for knowledge to grow, about what an amount of knowledge is, and about what it is for one amount of knowledge to be more or less than another, deep and interesting problems come to the surface. In this lecture I will explore this issue, examining and arguing against a very natural approach to understanding the measure or extent of one’s knowledge. The goal will be to give a sense of the shape and character of the problem, but equally to reveal how an adequate understanding of the quantitative dimension of knowledge rests on central issues in contemporary philosophy.