Homespun lapghan...need some help getting started

I have decided that I am going to make myself a lapghan out of Homespun. The problem is I am unsure as how many stitches to cast on. I am using size 11 needles and I want the finished size to be around 3 x 4 feet. I figured that I would knit up it up in squares. I came up with that size from the folded blanket I have on my lap while knitting and then rounding up. I have knit a couple of rows and so far do not have a problem with the Homespun.

Can anyone here help me out? Thanks a bunch!

Homespun is better on big needles, so you’ll be okay with it. Figure out how many inches you want each square to be then multiply that times your stitches per inch.