Consider the following.

We can calculate the height depending on initial height (ie thickness, denoted h\_0) and number of folds.

So, h(n) = h\_0 \* 2\^n

So, if you want to solve this for the number of folds, you get

log\_2 (h(n) / h\_0) = n

Now only plug in h(n) for the height you wanna calculate and h\_0 for the thickness of your "material".