A fitted sheet is a flat sheet with elastic sewn into the corners
A fitted bed sheet starts as a rectangle of fabric. You cut squares from each corner, fold the raw edges inward, insert elastic into the fold, and stitch it closed. The elastic pulls the corners tight so the sheet stays tucked under a mattress without sliding off. The process takes about two to three hours for a beginner and requires a sewing machine, elastic, and basic stitching skills.
The finished sheet fits a mattress because of how the corners are constructed. When you sew elastic into a folded corner pocket, that pocket becomes elastic too. When you stretch the sheet over a mattress corner, the elastic resists and holds the fabric in place. This is the only real difference between a fitted sheet and a flat one.
Key Takeaways
- Measure your mattress depth and add one inch before you cut corner squares, because the pocket depth determines how well the sheet stays tucked.
- Fold the raw edges of each corner pocket inward twice to hide the raw fabric, then stitch elastic into the fold using a zigzag stitch so the elastic can stretch without breaking the thread.
- Test the fit on your mattress before cutting and sewing the hem, because a corner pocket that is too shallow will slip off and one that is too deep will bunch.
- Use 1/4-inch-wide elastic rated for apparel, not wider craft elastic, because thinner elastic distributes pressure evenly and does not create hard ridges under the sheet.
Measure your mattress and cut corner squares
Start by measuring the depth of your mattress from top to bottom. A standard mattress is 8 to 12 inches deep, but yours may vary. Add one inch to this measurement—this extra inch becomes the seam allowance and the pocket that holds the elastic. Write this number down; you will use it to cut all four corners.
Lay your fabric flat on a large table or floor. At each corner, measure inward from the corner point a distance equal to your mattress depth plus one inch. Mark this point with a pen or chalk. Draw a square with sides equal to that measurement, then cut it out with scissors or a rotary cutter. You now have four identical squares removed from the corners, leaving a cross-shaped piece of fabric with four flaps.
Check your work by holding the fabric up to the mattress. The flaps should hang down the sides without bunching. If they are too short, your corner pockets will be too shallow and the sheet will slip. If they are too long, the pockets will be too deep and create bulk under the mattress. You can test this by folding one flap under and seeing how it sits on the corner.
Fold and pin the corner pockets
Take one corner flap and fold the two raw edges inward by 1/2 inch. Press the fold flat with your fingers or an iron. Fold those edges inward again by another 1/2 inch so the raw edges are completely hidden inside the fold. This double fold prevents fraying and creates a clean pocket opening where the elastic will go. Pin the fold in place with two or three pins.
Repeat this process on all four corners. Each corner should now have a neat fold running along both edges of the flap, with the raw fabric tucked inside. The fold should form a right angle at the corner point. If the folds do not line up evenly, unfold and repin—uneven folds will create a lopsided pocket.
Insert and stitch the elastic into the pocket
Cut a piece of 1/4-inch-wide elastic about 6 to 8 inches long. Thread it into the folded pocket opening at one corner, pushing it in with your fingers until it sits inside the fold. The elastic should run along the inside of the fold, parallel to the opening. Pin the elastic in place at both ends so it does not slip while you sew.
Set your sewing machine to a zigzag stitch at medium width and length. Zigzag stitching allows the elastic to stretch without the thread breaking. Sew along the opening of the pocket, stitching through the fabric and the elastic. Start at one end of the elastic and sew to the other end, keeping the needle about 1/8 inch from the edge of the fold. Backstitch at the beginning and end to lock the seam.
Repeat this process on all four corners. When you are finished, gently stretch each corner pocket to make sure the elastic moves freely and the stitches do not pucker. If a stitch line is too tight, the elastic cannot stretch properly and the sheet will not fit well.
Test the fit on your mattress
Before you finish the hem, put the sheet on your mattress to check the fit. Pull each corner pocket over a mattress corner and stretch it tight. The elastic should hold the fabric snug without the pocket bunching or the fabric pulling away from the corner. Walk around the mattress and check all four corners.
If a corner pocket is too shallow, the sheet will slip off when you move around in bed. If it is too deep, you will see wrinkles and folds under the mattress. If the fit is wrong, you can remove the elastic stitches with a seam ripper, adjust the pocket depth, and resew. It is much easier to fix this now than after you finish the hem.
Sew the hem around the edges
Once the corners fit properly, fold the outer edges of the sheet inward by 1/2 inch and press with an iron. Fold them inward again by another 1/2 inch to hide the raw edges. Pin the hem in place all the way around the sheet, including along the corner pockets.
Sew the hem using a straight stitch, staying about 1/8 inch from the folded edge. Sew slowly around the corners to keep the stitches straight. When you reach a corner pocket, the needle will go through both the hem and the pocket fabric—this is normal and makes the corner stronger. Backstitch at the beginning and end.
Press the finished hem flat with an iron. Trim any loose threads with scissors. Your fitted sheet is now complete and ready to use.
Common mistakes and how to avoid them
Corner pockets that are too shallow: This happens when you do not add enough to your mattress depth measurement. Measure twice and add the full inch before you cut. If you already cut and the pockets are too shallow, you cannot fix it without cutting new corners.
Elastic that breaks during sewing: This means you used a straight stitch instead of a zigzag. Straight stitches do not stretch, so they snap when the elastic moves. Always use zigzag stitching for elastic. If this happens, remove the stitches and resew with the correct stitch type.
Wrinkled or bunched corners: This usually means the elastic is too tight or the pocket is too deep. Test the fit on the mattress before finishing the hem. If the corners bunch, remove the elastic stitches, loosen the elastic slightly, and resew.
Raw edges showing at the fold: This means you did not fold the edges inward far enough before sewing. The fold should completely hide the raw fabric. If you see raw edges, you can fold the hem inward again and resew, or use a fabric pen to color the raw edge temporarily.
Frequently Asked Questions
What size elastic should I use?
Use 1/4-inch-wide elastic rated for apparel or swimwear. Wider elastic creates hard ridges that you can feel under the sheet, and narrower elastic may not hold the corner pocket securely. Avoid craft elastic or elastic meant for hair ties, as it is not designed for the repeated stretching that a fitted sheet experiences.
Can I use a regular straight stitch instead of zigzag?
No. A straight stitch does not stretch, so it will break when the elastic moves. Zigzag stitching allows the thread to flex with the elastic. If you do not have a zigzag stitch on your machine, you can use a stretch stitch or a narrow three-step zigzag, both of which are designed for elastic.
What if my mattress is thicker than 12 inches?
Measure your actual mattress depth and add one inch. If your mattress is 14 inches deep, cut corner squares that are 15 inches on each side. The process is the same; the pocket will straightforward be larger. Make sure your fabric is large enough to accommodate the bigger corners before you start cutting.
Do I need to pre-wash the fabric before sewing?
Yes, if you plan to wash the finished sheet. Pre-wash the fabric in warm water and dry it before you cut and sew. This prevents the sheet from shrinking unevenly after you finish it. If you skip this step, the sheet may pucker or the corners may become too tight after the first wash.
How do I fix a corner pocket that came loose?
Remove the stitches from the loose pocket using a seam ripper. Check that the elastic is still inside the fold and has not slipped out. Repin the pocket and resew it using a zigzag stitch, making sure the needle goes through all layers of fabric and the elastic. If the elastic has stretched out, replace it with a new piece.