The three seaming methods that work best for knitted fabric

The way you join knitted pieces depends on what you want the seam to look like and how much stretch you need it to have. The three methods that work for most projects are the mattress stitch (nearly invisible, used for side seams), the backstitch (visible but strong, used where durability matters), and the three-needle bind-off (used to join two live edges before you cast off). Each one uses the same basic tools—a tapestry needle and yarn that matches your project—but the technique changes where the needle goes and how tight you pull.

Mattress stitch is the most common choice for finishing sweaters and garments because the seam sits inside the fold of your edge stitches and becomes invisible once you wear the piece. Backstitch is faster and works well for seams that will be hidden, like the sides of a stuffed toy or the back of a blanket. Three-needle bind-off is used when you have two sets of live stitches waiting on needles and you want to join them without a separate seaming step.

Key Takeaways

  • Mattress stitch creates an invisible seam by running your needle through the loops on the inside edge of your knitted pieces, and works best on stockinette stitch fabric.
  • You should block your pieces flat before seaming so they are the same size and shape, which makes the seam sit evenly.
  • Backstitch is faster than mattress stitch but leaves a visible line, so use it for seams that will be hidden or where strength matters more than appearance.
  • Three-needle bind-off joins two live edges directly without a separate seaming step, and is often used to close the shoulders of a sweater.
  • The yarn you use to seam should match your project yarn in weight and color, and you should leave a long tail when you cast off so you have enough length to seam with.

How to do mattress stitch on stockinette

Thread your tapestry needle with a length of yarn about 18 to 24 inches long. Lay your two pieces flat on a table with the right sides facing up and the edges you want to join running parallel to each other, about half an inch apart. Insert your needle under the horizontal bar that runs between the first and second stitch on one piece, going from right to left under that bar. Pull the yarn through, leaving a 2-inch tail on the side you started from.

Move to the other piece and insert your needle under the same horizontal bar on that piece, again going from right to left. Pull the yarn through. Now go back to the first piece and insert your needle under the next horizontal bar up (the one between the second and third stitch), going from right to left. Pull gently. Repeat this pattern—one bar on the first piece, one bar on the second piece, moving up one stitch each time—for about an inch, then pull the yarn snug so the two pieces draw together. The seam will fold into the edge and disappear. Continue this pattern all the way up the seam, pulling snug every inch or so.

When you reach the end, weave your needle through a few stitches on the inside of the seam to anchor the yarn, then trim the tail. The seam should be nearly invisible from the outside.

How to do backstitch for hidden seams

Backstitch is the fastest seaming method and works well when the seam will not be seen. Place your two pieces with right sides facing each other (the sides you want to show on the outside are touching). Thread your tapestry needle with about 18 inches of yarn. Insert your needle through both layers about half a stitch in from the edge, going from back to front, and pull the yarn through, leaving a 2-inch tail.

Insert your needle back through both layers about half a stitch to the left of where you came out, going from front to back. Pull snug. Now insert your needle from back to front at a point half a stitch to the right of your last insertion point. Pull the yarn through. Repeat this pattern—going back half a stitch, then forward half a stitch—all the way along the seam. Each stitch should be small and tight. When you reach the end, weave your needle through a few stitches on the inside to anchor, then trim.

Backstitch creates a visible line on the inside of your seam, but because you are working with right sides together, that line stays hidden when you wear the piece. The seam is also very strong, which makes it a good choice for areas that get stress, like the underarms of a sweater.

How to do three-needle bind-off

This method joins two pieces that both have live stitches still on the needles—usually the two shoulder edges of a sweater. You will need two needles holding your stitches and a third needle to work with. Hold the two needles with live stitches parallel to each other with the right sides of the fabric facing each other. Insert your working needle through the first stitch on the front needle from left to right, then through the first stitch on the back needle from left to right.

Knit these two stitches together as one stitch, then repeat: knit the next stitch from the front needle and the next stitch from the back needle together. You now have two stitches on your working needle. Pass the first stitch over the second stitch to bind off, just as you would at the end of a normal row. Continue this pattern—knit two stitches together (one from each needle), then pass the first over the second—until all stitches are bound off. Cut your yarn and pull it through the last stitch to finish.

Three-needle bind-off creates a ridge on the inside of the seam, but it is very strong and it finishes the edges at the same time you join them, which saves a step. This method works best on shoulder seams where the ridge will not cause discomfort.

Blocking before you seam makes the work easier

Before you seam any pieces together, lay them flat on a blocking surface (a towel, a blocking board, or even a clean bed) and pin them to the shape and size they should be. Spray them lightly with water or steam them gently with an iron held a few inches above the fabric. Let them dry completely. This step, called blocking, evens out your stitches and makes sure all your pieces are the same size, which means your seams will sit flat and your finished piece will not have lumps or puckers.

Blocking is especially important if you are seaming pieces that have different stitch counts or if your tension was uneven while you were knitting. It takes a few hours for the pieces to dry, but it saves you from having to rip out seams later because they do not lie flat.

Choosing the right yarn and needle for seaming

Use the same yarn you knitted your project with, or yarn that matches it in weight and color. If your project yarn is thick or textured and hard to thread, you can use a thinner yarn in the same color—a fingering-weight yarn in the same fiber works well for seaming a bulky sweater. The thinner yarn will be easier to work with and the seam will be less visible.

Your tapestry needle should be large enough that the yarn slides through easily without splitting the fibers of your knitted fabric. A size 16 or 18 tapestry needle works for most projects. If your yarn is very thick, use a size 13 or 15. If your yarn is very thin, a size 20 or 22 will work. The needle should have a blunt tip so it does not pierce the yarn or the fabric.

What to do if your seam puckers or pulls

If your seam is pulling the edges together too tightly, you are pulling the yarn too hard as you seam. Loosen your tension—pull the yarn snug enough that the pieces draw together, but not so tight that the fabric bunches. If the seam is already done and it is too tight, you can carefully rip it out and redo it with a lighter hand.

If your seam puckers or waves, the pieces may not have been blocked before you seamed them, or one piece may be larger than the other. If you catch this while you are seaming, you can ease the larger piece in by taking slightly smaller stitches on that side. If the seam is already done, blocking the finished piece gently with steam can sometimes smooth out minor puckers.

Frequently Asked Questions

Can I use mattress stitch on ribbed or garter stitch fabric?

Mattress stitch works best on stockinette stitch because the horizontal bars are clear and straightforward to see. On garter stitch, the bumps are less defined, so backstitch is a better choice. On ribbed fabric, mattress stitch can work if you are careful to catch the bars between the knit and purl stitches, but backstitch is usually easier and faster.

How long should the yarn tail be when I cast off?

Leave a tail that is about three times the length of the seam you will be sewing. For a 12-inch seam, leave a 36-inch tail. This gives you enough yarn to seam without running out and having to join a new piece of yarn in the middle of the seam. If you do run out, you can weave in the end and start a new length of yarn by threading it through a few stitches on the inside.

What if I seamed two pieces together and they do not line up?

If the pieces are slightly off, you can sometimes adjust them by blocking the finished piece. If they are very misaligned, you may need to rip out the seam and redo it. To rip out a seam, use a seam ripper or small scissors to cut every few stitches, then pull the yarn out gently. Weave in the ends and start again, being more careful to match the stitch counts on each side.

Do I need to weave in the ends before or after I seam?

Weave in the ends after you seam. The tails from casting off are useful for seaming, and the ends from color changes or joining new yarn can be woven in once the seam is done. Weave them in on the inside of the seam or along the edge so they do not show on the outside of the finished piece.