Anyone Good With Math?

I am finishing up a tag cloud MOD for WWF forums, but the one problem I has is my weighting of tags for importance. Once we get a lot of tags into the database, it seems to work well, but in the interim the weighting is all off.

So for example, if I have 1 tag related to 3 posts, and 10 tags with one post each, my current algorithm will rank them the same, where the 3 post tag should be at the max size, but a month from now....it won't be.

Does that make sense?