Mattress stitch: how to seam knitting
Mattress stitch joins two pieces side by side, picking up the bar between stitch columns so the seam vanishes into the fabric.
Updated August 12, 2026·7 min read
Mattress stitch joins two knitted pieces edge to edge, working from the right side, picking up the little horizontal bar between the first two stitch columns on each piece. Pull it closed and the seam disappears into the fabric. It's the seam to use on sweater sides and sleeve seams.
You work it after both pieces are finished and blocked, with a blunt tapestry needle and a long tail of the same yarn.
Find the bars first
Lay one piece flat, right side up. Look at the column of stitches one full stitch in from the edge. Between that column and the next, running horizontally, is a small ladder of bars. Those are what you sew through. The very edge column is sacrificed into the seam allowance and is never picked up.
The steps
- 1Lay both pieces side by side, right sides up, edges touching, with the cast-on rows lined up at the bottom.
- 2Thread a tapestry needle with a tail of the working yarn, about three times the seam length.
- 3Anchor the bottom: bring the needle up through the corner cast-on stitch of the right piece, then the corresponding one on the left, and back again in a figure eight.
- 4Insert the tapestry needle under the first bar on the right piece, one stitch in from the edge, and pull the yarn through.
- 5Cross to the left piece and go under the matching bar there.
- 6Cross back to the right piece and pick up the next bar up.
- 7Keep alternating, two bars at a time on each side once you find your rhythm.
- 8Every inch or so, pull the seam yarn gently until the two edges close and the stitches meet. Firm, not tight — the seam should have the same stretch as the fabric.
Seaming different edges
| Joining | What to pick up | Notes |
|---|---|---|
| Side seam, stockinette | The bar between the first and second stitch columns | One bar per row on each side; the standard case |
| Garter stitch edges | The top loop of each edge bump, alternating sides | Garter rows are shorter, so match ridge to ridge, not row to row |
| Row edge to bound-off edge | Bars on the row-edge side, whole stitches on the bound-off side | Rows are shorter than stitches; expect roughly 3 bars to 2 stitches |
| Two bound-off edges | Not mattress stitch | Use three-needle bind-off or Kitchener stitch instead |
| Ribbing to ribbing | Bars, but plan the column so the rib pattern continues across the seam | Decide before you cast on which column gets eaten |
If it goes wrong
- The seam puckers and the garment won't lie flat.
- You pulled too hard. Mattress stitch should stretch with the fabric. Undo a few inches, redo them, and stop tightening once the edges just meet.
- One piece is riding higher than the other by the end.
- You skipped a bar somewhere, or picked up two on one side and one on the other. Check the row count on both pieces and match bar for bar. Fixing this means undoing back to where they diverged.
- A visible ridge shows on the right side.
- You're picking up the outermost column instead of the bar one stitch in. Move in by one full stitch.
- The seam gapes.
- Too loose. Tension it every inch as you go rather than at the end, when the slack has nowhere to redistribute to.
When not to use it
- Shoulder seams. Use a three-needle bind-off. Shoulders carry the garment's weight and want a firm, non-stretchy join.
- Sock toes and other live-stitch joins. Use Kitchener stitch, which grafts two sets of live stitches into an invisible row of knitting.
- Slippery or splitty yarn. Mattress stitch is fine, but seam with a smooth yarn in a matching colour instead of the project yarn if the project yarn keeps splitting.
Seam in good light, sitting at a table, with both pieces pinned flat. Everything about this technique gets harder on a sofa in the evening.