To follow up on the example -
7 strips at 2.5 inches/strip = 17.5 inches for straight grain - so you can get by with 1/2 yard.
7 strips at 2.25 inches/strip = 15.75 for straight grain - so you can breath easily with 1/2 yard.
I'm not sure how to translate to bias cut strips for the same amount of binding as so far I've only done bindings using straight grain.
I have a book on drafting quilts which is helpful in determining fabric amounts, and my favorite is Harriet Hargrave & Carrie Hargrave's books - Quilter's Academy series as they walk you through calculating fabric amounts.
Cheers, K