This was something i looked into during my first batch and was amazed at how many different ways people determine %ABV. I found a few that were middle of the road, took an average and that's what i use. I know, homebrewing and several different ways to do the same thing, go figure.
You'll also need to check the % attenuation of whatever yeast you end up using, along with aerating your wort sufficiently enough that the yeast can eat through all the sugar they are supposed to. Probably not as cut and dry as you would have liked, but I suppose if you just wanted to guesstimate the abv you could assume a FG of somewhere between 1.010 and 1.020 and do the calculations off of that.