The Beverage People in Santa Rosa is a fermentations supply house with lots of resources for wine and beer makers. They recently published a Harvest and Wine Math article available on their website. This guide has formulas for units of measurements, estimating yield from grape poundage, and making brix and acid adjustments.
Their website has more useful wine making articles including basic steps for red and white wine making, yeast and nutrient charts, sanitation, wine chemistry and more.