How to Work Mattress Stitch

Mattress stitch is a common way to finish seams on knitting projects. It gives the project a relatively seamless look on the front side and doesn’t leave a super bulky seam on the inside of your project.

What is Mattress Stitch?

Mattress stitch is a sewing technique whereby you join two pieces of knitting so that the stitches butt right up against each other, making it look more like one piece of uniform fabric.

Mattress stitch can be worked horizontally or vertically to seam the sides of a project, shoulder seams and other things that need to be held together.

It can be used any time the two pieces you are trying to join have the same number of stitches or rows.

Working Mattress Stitch Horizontally

Mattress stitch worked horizontally is most commonly used at the tops of garments to join the shoulder seams. This adds stability to the project that a garment worked in the round doesn’t have. You can also use it to sew knit blocks together when you’re working horizontally.

To start, you can use one of your yarn ends or thread a yarn needle with new yarn and weave it in a bit before you begin. I like to start with the working yarn on the right edge of the project, and working from the back, but you may find you like to do it a different way.

Orient the pieces you’re sewing together in the way you want them to be when the project is finished. Here I’m sewing together shoulder seams so the top piece is front side up and the bottom is front side down.

Take your needle through the edge stitch on the top layer or the opposite piece from where your yarn originates. You’ll go under the legs of the stitch as shown and pull through.

Repeat on the other side, making sure you’re going into the first stitch on the edge.

Continue across, working under the legs of each stitch on alternating sides. As I said I like to work from right to left so that’s what’s happening here.

Every inch/2.5 cm or so check that the tension on your sewing yarn is similar to the tension of the project. That is, the stitches you are forming shouldn’t be too tight or too loose compared to the fabric around them.

Work all the way across the seam and weave in your yarn end.

How to Work Mattress Stitch Vertically on Ribbing

Working mattress stitch vertically is how you sew the side seams of a project or the panels of a blanket together. It’s a similar technique but not quite the same. (Here I’m showing my argyle vest, which you may remember from my post on duplicate stitch.)

Here you want to arrange your pieces so that the front/outside is up on both pieces. It’s easiest to do this with your project sitting on a flat surface.

I like to work from the bottom up but you can go in whatever direction you like. Again, use the yarn tail or add in a new yarn to do your stitching. Here I wove in a new yarn using brown since the colors change on the front but not on the back. It shouldn’t be visible when the seam is done anyway.

I start by anchoring the pieces together by taking a stitch into the cast on/bind off on the piece the yarn is not already coming from.

These pieces happen to start with a purl stitch on one side and knit on the other, which is a little different from working just on stockinette. But it’s useful to know so we’ll go through it quickly.

Here I’m starting with a stitch on the purl side, so the needle goes under the purl bump in the bottom stitch of the fabric.

On the purl side you go into the v and under the yarn at the base of the v. If you pull gently on your knitting or stick your needle into the bottom of v, you’ll find a little piece of yarn there. That’s what you want to go under to make your stitch.

Continue stitching into one stitch on each side. In this photo you can see the yarn I used to sew a bit.

Once the ribbing portion is finished you can pull the yarn a little more tightly so the stitches butt up against each other better and the seam becomes invisible. Make sure you don’t pull too tightly so the seam lies flat.

Work Mattress Stitch on Stockinette Stitch

For mattress stitch worked vertically just on stockinette, you’re putting your needle into the v of the stitch on each side.

It’s up to you if you want to sew into the first stitch on each side or the second. It’s a little easier to see what you’re doing on the second stitch, because the first (or last) stitches of a row can sometimes be distorted. Whichever way you do it, be consistent across the seam.

Starting on the side opposite where your yarn is now, go into the first stitch and take the needle under that yarn in the middle of the stitch. Pull through, but you can leave it a little loose at this point. (If your project doesn’t start with ribbing you can begin your seam as above.)

Repeat on the other side. Do this for an inch/2.5 cm or so, then go back and pull the yarn a little more snugly to close up the seam and make sure the stitches are aligning properly. Don’t pull too tightly or the seam will pucker.

Continue in this manner for the length of the pieces you need to sew together.

If you find that you’ve gotten off track or one piece actually is longer than the other, you can fudge a little bit by taking your needle through two stitches at a time on the longer side. Don’t do this on every stitch, but you can do it every few stitches to help ease the pieces together.

Of course this won’t look perfect, but probably no one will be that close to your seams anyway. And if your pieces are wildly different sizes you may need to rip out some on the longer piece or knit more on the shorter piece so they are the same length instead of trying to fudge it.

Knowing how to work mattress stitch both ways gives you a way to finish projects so they look more seamless but still have the structure that seams provide. Do you have any tips for working mattress stitch? I’d love to hear them!