Depends on how much I sew...how much I have to UNsew, and what kind of stitch I'm using - decorative and zigzags use more thread than straight stitching, so for piecing, a bobbin lasts a while. I don't do very intricate quilting yet, but the most I've used for that is five bobbins to quilt one double size quilt. I don't think I've ever used 11 in two days! lol