The mattress stitch creates an invisible seam between shoulder pieces
The mattress stitch is the standard way to join shoulder seams in knitting because it produces a flat, nearly invisible seam that lies flush against the fabric. Unlike a backstitch, which creates a visible ridge, the mattress stitch works by catching the horizontal bars of yarn that sit between your edge stitches. The result looks like the two pieces were knitted as one.
You'll use this technique after you've finished knitting both shoulder pieces and bound off the stitches. The seam runs vertically along the edge where the two pieces meet, and you work from the right side of the fabric—meaning you can see exactly how the seam looks as you go.
Key Takeaways
- Thread a tapestry needle with yarn that matches your project, and work from the right side of the fabric so you can see the seam forming.
- Insert the needle under the horizontal bar between the first and second stitch on one piece, then under the corresponding bar on the other piece, moving up one row at a time.
- Pull the yarn snug every few rows—not so tight that the seam puckers, but tight enough that the edges draw together smoothly.
- The mattress stitch works best on pieces with straight edges and stockinette stitch fabric; garter stitch requires a slightly different approach.
What you need before you start
Gather a tapestry needle (also called a yarn needle)—a blunt needle with an eye large enough for your yarn. You'll also need yarn in a color that matches your project. Many knitters use the same yarn they knitted with, but if your working yarn is thick or textured, a thinner matching yarn works better and creates a less visible seam.
Lay both shoulder pieces flat on a table in front of you with the right sides facing up. Position them so the edges you're joining are parallel and close together, but not touching. Make sure both pieces are the same length; if one is longer, you may have a tension or row-count problem to fix before seaming.
Threading and anchoring your yarn
Thread the tapestry needle and tie a small knot at the end of the yarn. Insert the needle from the back of one shoulder piece, coming out at the base of the edge you're about to seam. Pull the yarn through until the knot catches on the back of the fabric—this anchors your thread so it won't slip out as you work.
You're now ready to begin the mattress stitch. The knot will be hidden inside the seam, so don't worry about it showing on the finished piece.
Working the mattress stitch row by row
Look at the edge of the first shoulder piece. You'll see a column of bumpy texture running along the edge—these are the stitches. Between each stitch is a small horizontal bar of yarn. Insert your needle under the horizontal bar that sits between the first and second stitch on the first piece, going from left to right. Pull the yarn through gently.
Now move to the second shoulder piece and insert the needle under the corresponding horizontal bar between the first and second stitch. Again, go from left to right and pull the yarn through. You've now completed one row of the seam.
Move up one row on the first piece and repeat: insert the needle under the next horizontal bar, then cross over to the second piece and insert under the bar in the same row. Continue this pattern, working your way up the seam. Every few rows—roughly every 4 to 6 rows—pull the working yarn snug to draw the two pieces together. The edges should come together smoothly without puckering or creating a ridge.
Tension and common mistakes
The most common mistake is pulling too hard on the yarn. If you cinch the seam tight after every row, the fabric will pucker and the seam will become visible rather than disappear. Instead, work loosely for several rows, then pull snug. This allows the yarn to settle naturally into the fabric.
Another frequent problem is skipping rows or working unevenly. If one shoulder piece has more rows than the other, you may need to skip a row on the longer piece occasionally to keep the seam straight and even. Count your rows as you go, especially on the first seam you attempt.
If you notice the seam starting to twist or angle to one side, stop and look at where you're inserting the needle. Make sure you're catching the bar directly between the first and second stitch, not drifting into the stitch itself.
Finishing the seam and weaving in the end
When you reach the top of the shoulder seam, insert the needle through the last few stitches on the inside of the fabric to find the thread. Make two or three small stitches in the same spot, then pull the needle out and trim the yarn close to the fabric. The end will disappear into the seam.
Step back and look at your work. A well-executed mattress stitch should be nearly invisible from the right side, with the two pieces appearing to flow into each other. If you see a visible line or ridge, you may have pulled too tightly or worked too loosely. This improves with practice—your second seam will look better than your first.
Adjusting the technique for garter stitch
If your shoulder pieces are knitted in garter stitch rather than stockinette, the mattress stitch works slightly differently. Garter stitch has a bumpy texture on both sides, and the horizontal bars are less obvious. Instead of catching the bar between stitches, you'll work under the bump of the stitch itself, moving up two rows at a time rather than one.
The principle remains the same—you're creating an invisible seam by working from the right side—but the rhythm is different. Practice on a small garter stitch swatch first if you're new to this variation.
Frequently Asked Questions
Can I use the mattress stitch on pieces with ribbing or cables?
The mattress stitch works best on flat stockinette edges. Ribbed or cabled edges have an uneven texture that makes it hard to find consistent horizontal bars. For these, a backstitch or a three-needle bind-off (if both pieces are still live stitches) is more reliable.
What if my shoulder pieces are different lengths?
Stop and check your gauge and row count before seaming. If one piece is genuinely longer, you can skip a row occasionally on the longer piece as you work up the seam, but this should be a last resort. Mismatched lengths usually mean a tension or pattern-reading error worth fixing.
How tight should I pull the yarn when I cinch the seam?
Pull just enough so the edges come together smoothly and the seam lies flat. You should not see a gap between the pieces, but you also should not see the fabric bunching or puckering. If you're unsure, err on the looser side—you can always tighten it slightly, but over-tightening is hard to fix.
Do I need to use the same yarn I knitted with?
No. If your working yarn is thick, textured, or splitty, a thinner yarn in the same color creates a less visible seam. Some knitters keep a small ball of smooth, thin yarn in common colors specifically for seaming.
What do I do if I make a mistake partway through the seam?
If you notice an error within a few rows, you can carefully pull the needle back out, undo those rows, and start again from where the seam was correct. For mistakes further back, it's often easier to finish the seam and accept the imperfection—seams are rarely scrutinized as closely as you think.