You're very limited by how wide you can go on straight ndls for blankets. You could opt to make strips and then seam them tog to get a full-size piece. To determine the size, did you do a swatch? Or, look at the piece you've worked. Determine how many sts are in an inch. Measure the # of sts over approx 4". Divide by 4. Example, 8 sts/4"=2. If 2 sts/inch, and you've CO 60, the piece would be 30" wide (60/2=30). If 1.5 sts/inch, it'll be 40" (60/1.5=40).