A wavy knit seam is fabric that was stretched while it was being sewn, and then stitched in that stretched shape.
Stop pulling. This is the main cause. Knits stretch under the slightest tension, and if you guide the fabric even gently faster than the feed dogs move it, the seam sets long. Let the feed dogs work and steer only.
Support the weight. A metre of jersey hanging off the table drags itself out of the machine. Keep the bulk on the table, not over the edge.
Fit a jersey needle. A universal point pierces the knit loop rather than sliding between the yarns, which causes skipped stitches — a separate fault, but it usually arrives at the same time.
Use a stitch with give. A narrow zigzag, about 0.5 to 1 mm wide and 2.5 mm long, or a dedicated stretch stitch. A straight stitch has no elasticity and the thread snaps the first time the seam is stretched.
Reduce presser foot pressure if your machine allows it. Too much pressure stretches the fabric as it feeds. This is the dial almost nobody adjusts and it is exactly what it is for.
If waves persist, try a walking foot, which feeds both layers at the same rate instead of letting the foot push the top layer forward.
Questions people actually ask
Do I need an overlocker for knits?
No. An overlocker is faster and gives a bought-garment finish, but a zigzag on a normal machine with a jersey needle holds perfectly well.
Why is my knit hem tunnelling?
Too much tension pulling the two rows of a twin-needle hem together. Reduce top tension, lengthen the stitch, and back the hem with a strip of stabiliser.
Last reviewed 2026-08-11