What you are actually sewing
A fitted sheet is a flat rectangle of fabric with four elastic-gathered pockets sewn into the corners. You are not sewing a complicated shape—you are sewing a straightforward flat sheet, then adding elastic to pull the corners into pockets that grip a mattress. The elastic does the work; your sewing just holds it in place.
The finished sheet will have a flat top edge (where you fold it over the mattress) and three sides with elastic casings that stretch around the mattress corners. If you have sewn a pillowcase or a straightforward seam before, you have the skills to do this. The only new technique is sewing a casing—a tunnel of fabric that holds elastic inside it.
Key Takeaways
- Cut your fabric to the mattress width plus depth plus 12 inches, on all four sides, then cut 4-inch squares from each corner.
- Sew the two short sides of each corner together with a 1/2-inch seam, creating four L-shaped seams that form the pocket shape.
- Fold the top edge down 1 1/2 inches and sew it flat, then fold it down again 1 1/2 inches and sew a casing that leaves a 1/2-inch opening for threading elastic.
- Thread 1/4-inch elastic through the casing at each corner, pull it tight enough that the pocket grips the mattress, and stitch the opening closed.
- Test the fit on your mattress before finishing the seams; if the pockets are too loose or tight, you can adjust the elastic before sewing it permanently.
Measuring and cutting your fabric
Measure your mattress width, length, and depth (the thickness). Add the depth to the width, then add 6 inches more for seam allowance and tucking. Do the same for the length. For example, a standard twin mattress is 39 inches wide and 75 inches long, with a 9-inch depth. Your fabric should be 39 + 9 + 6 = 54 inches wide and 75 + 9 + 6 = 90 inches long.
Cut a rectangle of fabric to those measurements. Then cut a 4-inch square from each corner—this is the piece you will remove so you can fold the sides up and sew them together. Mark the corners lightly with chalk or a fabric pen before you cut, so you know exactly where to remove the square.
If your fabric has a pattern or nap (like velvet or corduroy), lay it out so the pattern runs the same direction on all sides. Fitted sheets show the underside, so a directional pattern will look wrong if you cut corners from different directions.
Sewing the corner seams
After you cut out the four corner squares, you will have four L-shaped flaps at each corner. Fold one corner so the two cut edges meet at right angles, with the right sides of the fabric facing each other. Pin the two short edges together and sew them with a 1/2-inch seam allowance. Backstitch at the start and end so the seam does not unravel.
Repeat this for all four corners. You now have a fitted sheet shape—a flat rectangle with four sewn pockets instead of corners. Try it on your mattress to check the fit. The pockets should sit snugly at the corners without pulling the fabric tight across the top. If the pockets are too loose, you can make the seams slightly deeper (move the seam line inward by 1/4 inch) and re-sew. If they are too tight, let out the seams slightly.
Press the corner seams flat with an iron, then trim the seam allowance to 1/4 inch and finish the raw edges with a zigzag stitch or pinking shears. This keeps the seams from fraying when you wash the sheet.
Creating the elastic casing
The elastic casing is a tunnel sewn around the top edge of the sheet that holds the elastic in place. Fold the top edge of the sheet down 1 1/2 inches toward the wrong side (the side that will face the mattress) and press it flat with an iron. Fold it down another 1 1/2 inches and press again. You now have a 3-inch-wide fold at the top.
Pin this fold in place all the way around, then sew it down with a straight stitch 1/2 inch from the inner fold. This creates a casing that is 1 inch wide. Before you sew all the way around, leave a 1/2-inch opening on one side—this is where you will thread the elastic through. Backstitch before and after the opening so the stitches do not unravel when you pull the elastic.
Repeat this process on the three sides with the elastic pockets. The bottom edge (the side that will be tucked under the mattress) does not need a casing—you can finish it with a straightforward fold and stitch, or leave it raw and finish it with a zigzag stitch.
Threading and securing the elastic
Cut four pieces of 1/4-inch elastic, each about 18 inches long. Attach a safety pin to one end of the first piece and thread it through the casing opening you left on one side. Push the safety pin through the tunnel until it comes out the other end. Pull the elastic so it gathers the fabric evenly, then pin the two ends together so the elastic does not slip back out.
Try the sheet on your mattress. The elastic should pull the pocket tight enough that it grips the corner without sliding off, but not so tight that it distorts the fabric or makes the sheet hard to put on. If the fit is wrong, adjust the elastic length and try again. Once you are happy with the fit, sew the two ends of the elastic together with a zigzag stitch, then sew the opening in the casing closed with a straight stitch.
Repeat this process for the other three corners. Each corner gets its own piece of elastic, so you can adjust the tension at each one independently. A mattress is rarely perfectly square, so this flexibility is useful.
Finishing the edges and testing
Trim any loose threads and press the entire sheet with an iron. Fold it and try it on your mattress one more time. The pockets should grip all four corners evenly, and the top edge should lie flat without bunching. If one corner is looser than the others, you can open the casing at that corner, adjust the elastic, and re-sew it.
Wash the sheet in warm water with mild detergent before you use it. This shrinks the fabric slightly and sets the seams. Dry it on low heat or hang it to dry—high heat can damage the elastic and cause the fabric to shrink unevenly.
Common mistakes and how to avoid them
The most common mistake is cutting the corner squares too small. If the squares are smaller than 4 inches, the pockets will be too shallow and will not grip the mattress. If they are too large, the pockets will be too deep and will bunch up. Measure twice before you cut.
Another mistake is sewing the corner seams with the wrong sides of the fabric facing each other. The seam should be on the inside of the pocket (the side that touches the mattress), not on the outside. If you sew it backward, the seam will show and will be uncomfortable.
A third mistake is making the elastic casing too narrow. If the casing is less than 1 inch wide, the elastic will bunch up inside it and will not distribute the tension evenly. If it is more than 1 1/2 inches wide, the elastic will slide around inside the casing and will not stay in place. Measure the fold carefully before you sew.
Frequently Asked Questions
Can I use a different width of elastic?
Yes. Wider elastic (3/8 inch or 1/2 inch) distributes tension more evenly and is less likely to dig into the mattress. You will need to make the casing wider to fit it—a 1 1/2-inch-wide casing works well for 3/8-inch elastic. Narrower elastic (1/8 inch) works but is harder to thread and may not grip as firmly.
What if my mattress is thicker than 9 inches?
Measure your actual mattress depth and add it to your width and length measurements. A 12-inch-deep mattress needs 12 inches added to each dimension, not 9. The corner squares should still be 4 inches, but you may need longer elastic to reach around the thicker pocket.
Do I need a serger to finish the seams?
No. A zigzag stitch on a regular sewing machine works fine. Pinking shears also work—just cut the raw edges with the shears after you sew the seams. Both methods prevent fraying and are much cheaper than a serger.
Can I sew a fitted sheet by hand?
Yes, but it takes much longer. Use a backstitch for the corner seams and the casing, and make sure your stitches are small and tight so they do not unravel. Hand-sewn seams are actually very durable if you sew them carefully.
What fabric should I use?
Cotton percale and cotton sateen are the most common choices. Percale is crisp and cool; sateen is soft and silky. Both are durable and straightforward to sew. Avoid stretchy fabrics like jersey knit unless you are making a sheet for a foam mattress—the stretch can make the fit unpredictable.