Instructions
Measure the length and width of your quilt. Write down the numbers and indicate which is the length and which is the width.
Add the measurements together and multiply by two. The formula so far will be length + width x 2.
Now add 12 inches to the total. The formula for the full measurement will be length + width x 2 + 12. The result is the total length of binding that you need. The 12 inches is necessary to accommodate for the mitered corners and overlapping the edges to finish the quilt.
Use a ruler, or a scrap piece of fabric, to determine how wide of a border you think looks the best with the design of the quilt. Measure the width you have selected.
Multiply that width by four then add in twice the width of your seam allowance. For example if you are using a 1/2-inch seam allowance, add 1 inch to the width. When making a thick quilt, add an additional 1/4 inch to accommodate for the bulk of the quilt.