How to sew knit fabrics on a regular sewing machine

You can sew knits on any regular sewing machine. Use a ballpoint or stretch needle, polyester thread, and a stitch that stretches: a narrow zigzag (about 1 mm wide and 2.5 mm long) or your machine's stretch stitch. Lower the presser foot pressure or use a walking foot, let the fabric feed without pulling it, stabilize the seams that should not stretch, and hem with a twin needle or a zigzag.

Know your knit

A knit fabric is made of interlocking loops, so it stretches and does not fray. The common ones:

• Single jersey: smooth on the right side, small loops on the back, edges that curl. T-shirts.
• Interlock: smooth on both sides, more stable, edges that do not curl. Easier to sew.
• Rib knit: visible vertical ribs, very stretchy across. Neckbands, cuffs, fitted tops.
• French terry and sweatshirt fleece: a jersey face with loops or brushed fluff on the back. Sweatshirts and joggers.
• Elastane blends: any of the above with spandex added, which improves recovery, the way the fabric springs back after stretching.

Check the stretch percentage before cutting: hold 10 cm (4 in) of fabric across the grain between your fingers and stretch it gently along a ruler. If it reaches 15 cm (6 in), it has 50 % stretch. Knit patterns say how much stretch they need; a T-shirt usually needs at least 30 to 40 %, and bands need more.

Needles and thread

Use a good all-purpose polyester thread; it stretches more than cotton thread and is less likely to snap. Change the needle at the first skipped stitch or the first tiny hole along a seam.

Which stitch should I use on knits?

• Narrow zigzag: width 0.5 to 1.5 mm, length 2.5 mm (about 10 stitches per inch). Looks almost straight and stretches. The default if your machine has nothing else.
• Lightning stitch (stretch stitch): a slim zigzag shaped like a lightning bolt, designed for knit seams.
• Triple straight stitch: very strong and stretchy, but nearly impossible to unpick. Keep it for seams you have tested.
• Overlock-style stitch: sews and overcasts the edge in one pass, with its matching foot.
• Straight stitch: only where the seam must not stretch, such as a shoulder seam with stay tape in it, or for basting at 4 mm.

Sewly's knit patterns use a 1 cm (3/8 in) seam allowance by default, which suits these stitches. Sew the seam at the allowance with a narrow zigzag, then zigzag the two allowances together near the edge for a tidy finish if you like.

Machine setup

1. Fit the ballpoint or stretch needle.
2. Reduce the presser foot pressure if your machine has a dial: heavy pressure stretches knits and makes seams wavy.
3. Use a walking foot if you have one; it feeds the top layer at the same speed as the bottom one.
4. Test on a double layer of your actual fabric, cut in the same direction as the seam. Stretch the test seam: the thread should not crack.

How to sew a knit seam

1. Cut accurately. Use a rotary cutter if you can, and keep the whole length of fabric on the table: fabric hanging off the edge stretches. The grainline follows the ribs, with the most stretch going around the body.
2. Pin or clip. Use ballpoint pins or fabric clips, close together, without stretching the edges.
3. Start cleanly. Begin 5 mm (1/4 in) in from the edge, or on a small scrap, and hold the thread tails for the first stitches so thin knit is not pushed into the needle hole.
4. Let the feed dogs do the work. Do not push or pull the fabric. Support its weight so it does not drag behind the machine.
5. Stretch only on purpose. When attaching a neckband or a cuff, stretch the band, not the garment, to fit between pins.
6. Press gently. Use steam and lift the iron rather than sliding it. About 150 °C (300 °F) for cotton jersey with elastane, viscose and bamboo jersey, 110 °C (230 °F) for polyester and nylon knits; pure cotton jersey takes up to 200 °C (390 °F).

Stabilize the seams that should not stretch

Shoulder seams carry the weight of the garment and stretch out of shape over time. Sew a strip of clear elastic or stay tape into each shoulder seam, as Sewly's T-shirt pattern suggests in its notions. Necklines on loose knits can be staystitched with a narrow zigzag before the band goes on.

Neckbands

A knit neckband is cut shorter than the neckline so it pulls the edge in and lies flat. Sewly's T-shirt cuts it at 85 % of the neckline length, and its sweatshirt cuts the ribbing at 80 %, because ribbing is stretchier. Fold the band in half lengthwise, mark quarters on both the band and the neckline, match the marks, and sew with the band on top, stretching it evenly between the marks.

How to hem knits

• Twin needle: the ready-to-wear look. Press up the hem (2 cm or 3/4 in by default on Sewly knit patterns) and sew from the right side with a twin stretch needle, length 3 to 3.5 mm (7 to 8 per inch). The bobbin thread zigzags between the two rows underneath and gives the hem its stretch. See twin needle.
• Narrow zigzag: from the right side, close to the raw edge underneath, then trim the excess.
• Stabilized hem: a strip of lightweight fusible knit interfacing or hem tape inside the fold stops a twin-needle hem from tunneling, which is a raised ridge between the two rows.
• No hem at all: jersey does not fray, and a raw edge is a legitimate choice on casual tops.

Common mistakes and fixes

• Skipped stitches. Wrong or blunt needle. Switch to a stretch needle, try a size up or down, and rethread.
• Wavy, stretched seams. Too much presser foot pressure, or the fabric was pulled. Lower the pressure, use a walking foot, and steam the seam; cotton knits often shrink back flat.
• Holes along the seam or hem. A blunt or universal needle cut the loops. Fit a new ballpoint needle.
• Seams that pop when stretched. A straight stitch was used on a seam that stretches. Sew it again with a narrow zigzag or a stretch stitch.
• A tunneled twin-needle hem. Lower the needle tension slightly, lengthen the stitch, and stabilize the hem with fusible tape.
• Fabric eaten at the start of a seam. Start on a scrap of fabric or tissue paper, or begin a little in from the edge.

For a first knit project, a T-shirt in a stable cotton jersey or interlock with a little elastane is forgiving. If you are not sure whether your fabric is a knit, see woven vs knit fabric.