The mattress stitch is the strongest and least visible way to join shoulder seams in knitting

A mattress stitch (also called a ladder stitch) closes a knitted shoulder seam by threading yarn through the loops on the sides of your stitches rather than through the stitches themselves. The result is a seam that lies flat, stretches with the fabric, and is nearly invisible from the front. This is the method used in most professional knitwear because it holds up to wear and washing better than other seaming techniques.

You will need both pieces of your garment with live stitches still on the needles or held on stitch holders, a tapestry needle, and yarn in the same weight and color as your project. The seam works best when both sides have the same number of stitches and the same stitch pattern at the edge.

Key Takeaways

  • Mattress stitch uses the horizontal bars between stitches on the sides of your knitting, not the stitches themselves, so the seam stays flexible and invisible.
  • Both shoulder pieces must have live stitches on needles or holders before you start; binding off first makes the seam stiff and visible.
  • Thread your needle under two horizontal bars on one side, then two on the other side, in a back-and-forth pattern that creates a ladder inside the seam.
  • Pull the yarn snug every few inches so the seam closes invisibly, but not so tight that it puckers or restricts the stretch of the fabric.
  • A 24-inch length of yarn is usually enough for a shoulder seam; if you run out, weave in the end and start a new length rather than using a very long strand that tangles.

Set up your pieces and thread your needle

Place both shoulder pieces on a flat surface with the right sides facing you and the live stitches at the top. If your stitches are on needles, you can leave them there or slip them onto stitch holders—either works. The key is that the stitches stay live (not bound off) so the seam can thread through them.

Cut a length of yarn about 24 inches long and thread it onto a tapestry needle. A tapestry needle has a blunt tip and a large eye, which prevents you from splitting the yarn or accidentally piercing through stitches. If you do not have a tapestry needle, a size 16 or 18 blunt needle works in a pinch.

Insert the needle and begin the ladder pattern

Start at the right edge of the right shoulder piece. Insert your needle under the first horizontal bar (the strand of yarn that runs horizontally between the first and second stitch on the edge of your knitting). This bar sits just below the needle or stitch holder. Pull the yarn through, leaving a 2-inch tail on the left side of the seam—you will weave this in later.

Move to the left shoulder piece and insert the needle under the first horizontal bar on that side as well. Pull the yarn through. Now move back to the right piece and insert the needle under the next horizontal bar down. Then move to the left piece and insert under the next bar down. You are creating a ladder of yarn inside the seam, with the yarn running back and forth between the two pieces.

Continue this pattern for about 1 inch or 4 to 6 bars on each side. Do not pull the yarn tight yet—keep it loose so you can see the ladder you are building.

Close the seam by pulling the yarn snug

Once you have worked about 1 inch of the ladder, gently pull the working yarn (the end still attached to the ball) upward. The two sides of your knitting will draw together and the ladder will disappear inside the seam. The seam should close invisibly, with no gap between the two pieces and no visible yarn on the front.

Pull until the seam is snug but not tight. If you pull too hard, the seam will pucker and the fabric will lose its stretch. If the seam is too loose, it will gape and look unfinished. The right tension feels like the seam is closing smoothly without any resistance.

Once the seam is closed, continue the ladder pattern for another inch, then pull snug again. Repeat this process—work about 1 inch of ladder, then close—all the way up the shoulder.

Finish the seam at the neckline

When you reach the top of the shoulder and have only a few stitches left, work the ladder through the remaining stitches. You may need to work under just one bar per side for the last stitch or two, depending on how many stitches you have.

Once you have worked through all the stitches, pull the yarn snug one final time. Insert the needle through the last stitch on the left piece, then back through the last stitch on the right piece, to anchor the seam. Pull the yarn tight and weave the end through the seam for about 1 inch, then trim.

Go back to the beginning of the seam and weave in the 2-inch tail you left at the start in the same way—thread it through the seam for about 1 inch and trim.

Check your work and block if needed

Turn your garment over and look at the seam from the back. You should see a neat line of horizontal bars running up the center of the seam. From the front, the seam should be nearly invisible, with no ridge or gap. If you see puckering or a tight line, the seam was pulled too snugly; this usually relaxes a little after washing and blocking.

If your seam looks loose or gappy, you can tighten it by going back and pulling the yarn snug in sections. Work from the bottom up, pulling each section of the ladder closed again. This is one advantage of mattress stitch—you can adjust the tension after the fact.

Wet blocking (soaking the garment in cool water, then laying it flat to dry) helps even out the seam and relax any tension. This step is optional but recommended for garments that will be worn close to the body, like sweaters.

Troubleshooting common seaming problems

If your seam is visible from the front, you may have been working through the wrong bars. The horizontal bars should be on the very edge of your knitting, one stitch in from the edge. If you are working one stitch too far in, the seam will show. Rip back and start again, making sure to insert the needle under the outermost bar on each side.

If the seam is too tight and restricts the stretch of the fabric, you pulled the yarn too snugly. Rip back a few inches, loosen the tension, and redo that section. Mattress stitch should feel as stretchy as the rest of the fabric.

If you run out of yarn before reaching the top, weave in the end and start a new length. Insert the needle under a bar on the right side, pull the new yarn through, and continue the ladder pattern as if you had never stopped. The join will be invisible once the seam is closed.

Frequently Asked Questions

Can I use mattress stitch if I have already bound off the stitches?

Mattress stitch works best with live stitches because it threads through the bars between stitches. If you have already bound off, you can use a backstitch or whip stitch instead, but the seam will be stiffer and more visible. For future projects, leave the stitches live until you are ready to seam.

What if the two shoulder pieces have different numbers of stitches?

If one side has one or two more stitches than the other, you can skip a bar on the side with more stitches to even things out. Work under two bars on the side with fewer stitches, then under three bars on the side with more stitches, to keep the seam straight. If the difference is more than two stitches, the pieces may not fit together evenly and you may need to rip back and reknit.

How tight should the seam be?

The seam should be snug enough that there is no gap between the two pieces, but loose enough that it stretches as easily as the rest of the fabric. If you have to force the needle through or the seam looks puckered, you are pulling too hard. Aim for a seam that feels like part of the garment, not a separate element.

Do I have to weave in the yarn ends right away?

No. You can leave the tails hanging and weave them in after you have blocked the garment. Some knitters find it easier to weave in ends after blocking because the fabric is more stable. Just make sure the tails are long enough (at least 2 inches) that they do not slip out before you weave them in.

Can I use mattress stitch on other seams besides shoulders?

Yes. Mattress stitch works on side seams, sleeve seams, and any seam where you have live stitches on both sides. It is the standard seaming method in knitting because it is strong, invisible, and flexible. The technique is the same regardless of which seam you are closing.