we actually use google as well, but it is basically the same as excel. Either way...
we have ours setup with basically two sections per style, one very basic section that is essentially just for quick reference, with current stock and "ideal" stock, then it uses those to generate what we need to order (and there is some info on pricing etc. to determine when it makes sense to order stuff). We order when it gets low or we run out or the formula says we should (lol). The second section is larger and related to sales over time and has a lot more complex formulation to show us different things. I guess there is kind of a third section with a bunch of random weird calculations we have done on a whim, and when we find we reference one enough it gets put in section two and cleaned up and labeled clearly.