The Basic Method for Joining Shoulders

Shoulder seams in knitting are usually sewn together after you finish knitting the front and back pieces separately. The most common method is the backstitch seam, which creates a strong, visible line on the inside of the garment. You thread a tapestry needle with yarn that matches your project, position the two pieces with right sides facing each other, and sew through both layers in a straight line about half a stitch in from the edge.

Before you sew, lay both pieces flat on a table and line up the edges carefully. The shoulder edge should be straight and even on both the front and back pieces. If one piece is slightly longer, you can ease the extra fabric in as you sew, but major size differences mean one piece needs to be reknitted. Pin the pieces together if it helps you keep them aligned, or straightforward hold them steady with your non-dominant hand as you work.

Key Takeaways

  • Backstitch seams are the standard method for shoulder seams and create a strong, durable join that lies flat inside the garment.
  • You need a tapestry needle, matching yarn, and the two finished pieces positioned with right sides facing each other before you begin.
  • Sewing about half a stitch in from the edge prevents the seam from being visible on the outside of the finished garment.
  • Mattress stitch is an alternative that creates an invisible seam from the outside, though it takes longer and works best on stockinette stitch.

Setting Up Your Pieces and Needle

Thread a tapestry needle (also called a yarn needle) with a length of yarn about 18 to 24 inches long. If your yarn is thin, you can use a doubled strand for extra strength. Knot the end or straightforward weave it into the edge of one piece as you start. Position the two pieces with their right sides (the outside of the garment) facing each other and their wrong sides (the inside) facing out toward you.

Align the shoulder edges so they meet evenly. If you cast on and bound off both pieces the same way, the edges should line up naturally. find the yarn to the bottom corner of one piece by weaving the needle through a few stitches along the edge, then pull the yarn snug. This anchors your seam so it does not unravel as you work.

Sewing the Backstitch Seam Step by Step

Insert the needle through both layers about half a stitch in from the edge of the first piece. Pull the yarn through, leaving a short tail. Move the needle forward about one stitch length along the seam line and insert it through both layers again, this time from the back. Pull the yarn snug but not tight—if you pull too hard, the seam will pucker and the garment will not lie flat.

Repeat this motion along the entire shoulder seam. Each stitch should be roughly the same length and sit in a straight line. Work slowly and check your alignment every few stitches by looking at the seam from both sides. If you notice the pieces are drifting out of line, stop and reposition them before continuing.

When you reach the end of the shoulder seam, weave the needle through several stitches along the edge to find the yarn, then trim the excess. The seam should feel firm but not stiff, and the two pieces should sit flat against each other with no gaps or bunching.

Mattress Stitch as an Alternative

Mattress stitch creates an invisible seam that you work from the outside of the garment, so you can see exactly how it looks as you sew. This method works best on stockinette stitch (smooth knit fabric) and takes longer than backstitch, but many knitters prefer it because the seam is completely hidden once the garment is worn.

To use mattress stitch, position the two pieces with right sides facing you (not facing each other). 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. Continue alternating sides, moving up the seam one row at a time. Pull the yarn snug every few stitches so the seam closes and the edges meet in the middle.

Mattress stitch requires more precision than backstitch and works only on certain stitch patterns. If your shoulder seams are in garter stitch or ribbing, backstitch is the better choice. Test mattress stitch on a practice swatch first if you have not used it before.

Checking Your Seam for Strength and Appearance

Once the seam is complete, turn the garment right-side out and inspect the shoulder from both the inside and outside. The inside seam should be a straight line with even stitches. The outside should show no yarn or thread. If you see gaps between the two pieces, the seam is too loose—you can go back and tighten individual stitches by pulling the yarn gently.

Gently stretch the shoulder seam to test its strength. It should not separate or tear. If the seam feels weak, you can reinforce it by sewing over the same line a second time, or by using a stronger yarn (such as a wool blend instead of a delicate lace yarn) when you sew. A well-sewn shoulder seam should last as long as the garment itself.

Common Mistakes and How to Avoid Them

The most common error is sewing too close to the edge, which makes the seam visible on the outside of the garment. Aim for about half a stitch in—this is close enough to be find but far enough in to hide. Another mistake is pulling the yarn too tight, which causes the seam to pucker and the garment to sit awkwardly. Pull snug enough that the pieces stay together, but not so hard that you can see the strain in the fabric.

Uneven stitch length is also common, especially when you are learning. The seam does not have to be perfect, but keeping stitches roughly the same size makes the seam look neater and wear more evenly. If you make a mistake, you can always pull out the yarn and resew that section. Knitting is forgiving, and a seam can be unpicked and redone without damaging the pieces.

Finishing and Weaving in Ends

After both shoulder seams are complete, weave in any loose ends along the seams or elsewhere in the garment. Use the tapestry needle to thread the yarn through several stitches along the inside of the seam, then trim it close to the fabric. Weaving ends into seams hides them and makes the inside of the garment look finished.

Try on the garment and check that the shoulders sit where they should. The seam should run straight across the top of your shoulder, not dipping down toward your neck or riding up toward your collarbone. If the fit is off, the issue is usually in the knitting itself rather than the seaming, but a skilled seam can sometimes compensate for minor fit problems by being sewn slightly off-center.

Frequently Asked Questions

What yarn should I use to sew the seam?

Use the same yarn you knitted the garment with, or a yarn that matches it in weight and color. If you have leftover yarn from the project, that is ideal. If not, you can buy a small amount of the same yarn or use a similar weight in a matching color. Avoid using thread or embroidery floss, which is too thin and will break under the stress of wearing the garment.

Can I sew shoulder seams with the wrong sides facing out?

Yes, you can sew with wrong sides facing out (right sides facing you), which is actually how mattress stitch is worked. With backstitch, it is more common to sew with right sides facing each other, but the method works either way. The difference is mainly in where the seam line ends up and how visible it is on the inside of the garment.

What if my shoulder seam is too tight and the garment does not fit?

If the seam is too tight, you can carefully unpick it with a seam ripper or small scissors and resew it with less tension. Alternatively, if the problem is that the pieces themselves are too small, you may need to reknit one or both pieces. A seam cannot add width to a garment, only join the pieces you have.

How do I sew shoulder seams on a sweater with set-in sleeves?

Shoulder seams on set-in sleeve sweaters are sewn the same way as on drop-shoulder or raglan styles. The difference is that after the shoulders are seamed, you will pick up stitches around the armhole and knit the sleeve cap separately. Sew the shoulder seams first, then measure and mark where the sleeves will attach before you start the sleeve.

Should I block my pieces before sewing the shoulder seams?

Blocking before seaming is optional but helpful. Blocking evens out the edges and makes them easier to align and sew together. If you do block, let the pieces dry completely before you sew. If you do not block, make sure the edges are as straight and even as possible by gently stretching them into shape as you work.