Things You'll Need
Sharp sewing scissors
Sewing ruler or yard stick
Matching or contrasting fabric of your choice
Edge stitching foot for your sewing machine
Perhaps you just purchased a new mattress and it's a little more plush than your last. Maybe you used too high a heat setting on the dryer and you shrunk your fitted sheets. Rather than tossing your sheets out, you can enlarge them yourself if you feel confident with a sewing machine and have mastered some basic seamstress skills such as sewing seams and working with elastic. If you take advantage of your fabric store's seasonal promotions, you may be able to score a few yards of fabric at a good price and make this an economical way to extend the life of your bedding or add a little color to your ho-hum sheets.
Wash, dry and iron your sheet and new fabric.
Remove your sheet's existing elastic by unpicking the corner seams using a seam ripper. You will be left with a rectangle that has four squares cut out from the corners.
Cut off the flaps on the corners using a straight edge to guide you for an even cut. You will be left with a perfect rectangle.
Add the matching or contrasting fabric around the outside edge of the rectangle to create a bigger rectangle. Your particular needs and the shortage you are compensating for will dictate how much excess fabric you should add.
Approximately 16-inch width of material is needed to create a standard-sized pocket to wrap around and under your mattress. You may need considerably less if you just want to add a little extra depth in your sheet to correct a shrinkage or to accommodate a more plush mattress.
Sew the new material onto the outside edge of your existing sheet using a ¼-inch seam allowance.
Fold your sheet in half inside-out and line the corners on top of each other. Measure and mark a 16-inch square on the top right and left corners of the sheet (be sure you don't cut the folded side, but where the top and bottom edges of the sheet meet). The size of your square will dictate the depth of your pocket. Carefully cut out your marked corner pieces using your sewing scissors.
Unfold the sheet and create four corner pockets by stitching together each set of flaps made when you cut into the fabric. Use a ¼-inch seam allowance on your sewing machine. Pinning the flaps before sewing them together may be helpful to keep things aligned while you work.
Cut a piece of elastic for the size of bed you have: king, 45 to 50 inches; full or queen, 40 inches; twin, 30 to 35 inches. Mark your elastic placement 10 inches from the corner point on each side. Where your elastic will be placed, create your seam with an iron first by ironing a ½-inch seam before rolling it inside and ironing a second seam ¼-inch deep. Pin where needed to secure.
Line up the edge of your elastic with your first mark and make a couple of stitches to secure it in place. Using an edge stitching foot on your sewing machine, sew your seam from corner to corner of each pocket and along the side seam while gently tugging the elastic to create a pucker.