The Binding Miter Tool Tutorial
A folded, straight of grain binding is great for quilts with straight sides. Cut strips of binding fabric 2-1/2" wide and stitch them together, end to end, to the length needed for each side. Each piece of binding needs to be 3" longer than the quilt. Press the seams open, and press these long strips in half lengthwise, right side out.
With the quilt still on the floor from the blocking, but definitely dry, lay the two long binding strips across the length of the quilt in the center just like you measured the borders. Leaving 1-1/2" of 'tail' above the quilt, place a pin through the binding, even with the top raw edge of the quilt. Carefully smooth the bindings across the quilt, to keep them smooth, and place a pin through them even with the bottom raw edge. There should be at least a 1-1/2" 'tail' remaining.
Keeping the two bindings together without slipping, remove one end and insert a second pin in the same spot so both binding strips will be marked. Do the same at the other end.
Similarly mark the bindings for the top and bottom through the middle of the quilt.
Pin each binding in place, keeping the raw edges of the binding even with the raw edge of the quilt. Use several pins on each side so nothing shifts or moves.
Stitch the bindings to the quilt with 1/4" seams, starting and stopping at the 1/4" seam allowance at each corner. Trim any excess backing and binding fabric so they extend about 1/4" beyond the edge of the quilt.
To miter the corners of the bindings, fold the quilt back upon itself at a corner so the binding from the side is lying exactly on top of the top binding.
Place a mark on the fold of the binding straight above the place where the stitching ended. Using the corner of a ruler (or my Binding Miter Tool which was designed to make this easy!) point the corner toward the binding tails, and center it so the distance from the ruler's corner is the same to the stitching line as it is to the mark on the fold.