I would begin by thinking about whether or not I wanted pieced borders. I don't like them, but I have seen borders pieced and it doesn't take away from the quilt at all. If no pieced borders, you'll need a cut as long as your longest side, so roughly two yards or slightly more for the first and then 1 3/4 yard for the second.
Just my thoughts. If piecing, then I'm not sure. I always buy too much anyways so you probably shouldn't listen to me anyways!