# Length of a dimension?

I am really confused about what is the minimum length for a dimension to exist (I don't know the exact word). Like I mean, we call the paper to be a 2 dimensional object but if we magnify its edges, we have the third dimension as well.

So my question is, for example, what should be the minimum breadth of the edge of the paper so that we can say that the paper is only 2 dimensional?