To make mitered quilt corners, first sew the fabric for the border to each side of the quilt, stopping and starting 1/4 inch away from each end. Next, fold the quilt top diagonally, making sure the edges and corners of the quilt top are lined up. With a ruler and pencil, draw a 45-degree line on the border from the seam to the edge. Pin the fabric firmly, and sew along the line. Repeat with the other corners.
In order to calculate the amount of fabric needed for the border, first measure the length of one side of the quilt. Next, measure the width of the border, and multiply that by two. Add the length of the side to the width of the border, and add 6 inches to the result. Repeat this for each side of the quilt.
Before trimming and pressing the finished corners, thoroughly check the quilt for any gaps or odd places. Only when you are satisfied with the quilt should you then trim and press the border.
Mitering a quilt border results in the corners meeting at a 45-degree angle. Though this quilt technique can be a little difficult, accurate measuring and sewing results in a neatly finished product.