Measure around the edges of the blanket. You need to know this measurement so you can buy the correct amount of binding. Binding is sold in packages that generally have 4 yards in them, so convert your measurement to yards. If your blanket is in between yardage amounts, always go with more. For instance, if your blanket has 5 1/2 yards of edge, you need to get 6 yards of binding.
Spread out the blanket, right side up, on a flat surface. Slip the binding over the edge of one corner of the blanket, placing the narrow side of the the binding on top of the blanket and the wider side underneath the blanket. Pin the binding into place with straight pins along the entire first side of the blanket.
Fold the edging around the blanket corner. Notice the triangle of binding that sticks out on either side of the blanket. Tuck the triangle inside the binding on each side, as if making a bed, to miter the corner. Pin into place.
Keep pinning the binding along the sides of the blanket and mitering the corners until you reach your starting point. At the starting point, pin the binding so it looks like the other mitered corners. Trim away excess binding.
Stitch the binding into place by hand or on a sewing machine. Use any stitch that you like, from a basic running stitch to a decorative zig-zag. Trim away thread ends when finished.