When hemming two edges that meet, the multiple folds along each edge pile up on top of each other and create an excess of fabric at the corner. Mitered corners reduce the bulk, allow the edges to meet evenly, and look oh-so-satisfyingly neat and tidy.
Here are two different methods for making mitered corners.
On all edges, press half your hem allowance to the wrong side.
Press the same amount again. At the corners, make sure you fold and press evenly. It will be bulky.
Find the middle square formed by the folds. Mark a line through its corners all the way across as shown.
Trim along line.
Fold angled edge in so that the creases line up with each other. The creases you should be aligning are marked in blue. Press lightly, taking care not to press out your other folds.
Refold along first fold and press.
Refold along second line and press.
Pin corner and sew around inner fold, pivoting in mitered corner directly between folds.
Sewn and Topstitched
This form of mitered corner is stronger and will stand up to more wear and tear.
First, divide your hem allowance in two parts. You can divide it evenly, or, for a wider finished hem, divide it into a smaller and bigger portion. (For example, if my hem allowance is 1″, I can either divide it into 1/2″ and 1/2″, or 1/4″ and 3/4″.)
Press half your hem allowance towards the wrong side along both edges. If you divided your hem unevenly, press the smaller portion.
Press half your hem allowance towards the wrong side again. If you divided your hem unevenly, this time press the larger portion.
Unfold the second fold only. Fold the corner in towards the wrong side as shown so that the creases line up with those from the second fold. The creases we are aligning are traced in blue.
Press to crease and unfold.
Now fold the corner right sides together, aligning the outer edges. You should be folding so that the most recent crease – the one diagonally across the corner – is lined up with itself through the layers. This crease is marked in blue. Pin.
Stitch along crease, backstitching at beginning and end. Cut off excess and clip top corner.
Turn corner right side out and use point turner or chopstick to push it out.
Press, then topstitch around free inner fold, pivoting at the corner.