So I'm making one or possibly two (probably identical) quilts for my mother to use as bedspreads in their new guest room. I'm currently really in love with the log cabin block and would like to make a quilt based on that. I've selected some gray-blue fabrics and some beige-brown ones and I'm thinking blocks with the one half based on three gray-blue fabrics and the other half the beige-brown ones, the strips about an inch wide after sewn togeher (so I would cut them 1.5" wide). (Middle one will be whitish, I think.) Now. My problem is I have no clue whatsoever how much fabric to get!!

Is there any way to calculate that using the info here? I don't even know where to start... The beds are regular (twin?) beds set against walls, not big or anything, but the quilt should hang down some on the side of the bed that is facing the room. I'm thinking I might sash the quilt (but not the blocks) with coordinating fabric.

ANY help is most welcome! I'm going to order the fabric online for DH to bring home when he's over there in a couple of weeks, so it will be hard to get more of the same fabric later...