Sewing miter corners will give your project a finished, professional appearance. While miter corners may sound scary, they really aren't that hard to do with a little time and practice. And, miter corners really do cut back on the decidedly bulky appearance that corners can have.
Sewing Miter Corners
Using an iron, press your desired hem into the fabric. For purposes of discussion now, think in terms of an overall one inch hem with a one-quarter inch fold underneath. After you finish ironing, you should have corners with heavy fabric overlaps.
Take two straight pins and mark where the two overlapping pieces touch each other at the point farthest from the corner. You will end up with one pin marking the intersecting point on the upper piece of folded fabric and the second pin marking the intersecting point on the lower piece of folded fabric.
Next, open up the hem, but leave the one-quarter inch fold alone. The wrong side should be face out. Turn the fabric back on itself until the quarter inch folds match up on one side and are even. You should see a sort of triangle effect and the pins should be in line with each other.
Draw a line that runs through the pins to the sides of the fabric across from them. You will now have marked the triangle piece that you will trim from the fabric.
However, before you grab your scissors, sew across the line that you have drawn. Then, check to see how the miter looks. If it looks good, turn the fabric out and trim the triangle with a quarter inch seam allowance. If the miter doesn't fit, rip it out and try again.
If you are good to go, iron the miter seam open after you have cut off that triangle. Then, you just have to finish sewing your hem.
You may now admire your work.