A yard seems like a lot to me, but it depends on how you want to cut the binding piece, whether in a square or rectangle, and whether you're using the continuous binding method (which I gather you are not). For bias you don't really have to cut absolutely on the 45 degree diagonal, since you will have the bit of stretch you want even if you're cutting somewhat off, say at 30 degrees for example. Most of the calulators assume you are cutting at 45 degrees.
Here is one online calculator -
http://www.quiltersparadiseesc.com/C...Calculator.php