Mason Dixon KAL

The fact that these will be mitred squares doesn't make any difference to the calculations (Unless you are working in stripes when you might need to allow extra for all the ends). What matters is the area you want to cover.

One of the easiest ways, to avoid most of the calculations, is to knit one square and see how much it takes.

You could knit a square, pull it undone, and measure the yarn used.

Alternatively, put markers on the yarn before you start. Every metre/yard/5 yards/whatever unit you choose, push a small length of contrast yarn between the plies of your yarn. As you knit, remove these markers. Count the markers when you've finished and you will know how much you used for one square.

Multiply by the number of squares to find the total. Remember to add extra if you are adding a border.
 

Thanks all for your help. The advice to knit up the square would slightly defeat what I was asking as I dont have the yarn yet, that was what I was trying to figure out, how much to buy initially. I'm just going to get 2-4 balls, I havent decided yet, in a color I really like if I have to much and hope its enough. This project might get put on hold temporarily for a March b-day instead of a Dec holiday gift. Thanks again for all your help.