There are times when quilting that you will need to sew a mitered corner. If you’re new to quilting, here is how I handle the job using a white square and brown border strips.
Place a strip of fabric on top of the square or rectangle to be bordered, right sides together. Make sure the border strip to be mitered extends over the edge of the square or rectangle enough to create the miter. Sew with a quarter-inch seam along the straight edge stopping one-quarter inch from the end. Repeat with the fabric strip along the opposite side of the corner. Press seams towards the fabric strip. In these photos, you are looking at the wrong side of the fabrics. Notice in the second photo that the corners are not sewn down.
Line up the edge of your ruler along one of the strips and with a chalk or marker, draw the line on the overlapping strip. Repeat with the other strip.
Fold one strip over the other strip as shown in photo. The square or rectangle in the center will have a diagonal fold. Place your ruler along the diagonal. Draw a line from the intersection of the corner seam to the point at which the strips meet (where you traced the lines earler). Pin in place with two or three pins. Sew along the drawn line.
Open and press the miter to one side. Trim away the excess fabric one-quarter inch from the seam. Voila! You have made a mitered corner!