T-shirt seams and hems go wavy when the fabric is stretched as it feeds through the machine. To stop it, choose a stable cotton-elastane jersey of 180–220 GSM, use a ballpoint or stretch needle (75/11 or 80/12), sew with a narrow zigzag or stretch stitch about 2.5–3 mm long, lower the presser foot pressure or use a walking foot, let the machine feed the fabric without pulling it, and stabilize hems with a strip of fusible tape.
Which jersey should a beginner buy?
Not all jersey is equally easy. Jersey is a single knit: smooth on the front, with little loops on the back, and its cut edges curl. Its friendliest versions contain a little elastane and have enough weight to lie flat.
| Knit | Weight | Stretch | For beginners |
|---|---|---|---|
| Cotton-elastane jersey (around 5% elastane) | 180–220 GSM (5.3–6.5 oz/yd²) | 40–60%, good recovery | Best start for T-shirts |
| Cotton jersey (no elastane) | 140–180 GSM (4.1–5.3 oz/yd²) | 20–30%, little recovery | Fine, but curls more |
| Interlock | 180–250 GSM (5.3–7.4 oz/yd²) | 30–50% | Easy: does not curl |
| French terry | 240–350 GSM (7.1–10.3 oz/yd²) | 20–40% | Easiest knit, for sweatshirts |
| Rib knit | 200–300 GSM (5.9–8.9 oz/yd²) | 60–100% | For neckbands, cuffs and hem bands |
| Viscose or bamboo jersey | 160–220 GSM (4.7–6.5 oz/yd²) | 50–70% | Drapey and slippery: try it later |
For a first T-shirt, buy a solid or a small print. Stripes look great but show every off-grain cut and every seam that does not match.
How do you measure how much a knit stretches?
Knit patterns state a minimum stretch percentage. To test your fabric, fold it along a crosswise line and mark 10 cm (4 in) on the fold. Hold one mark still and stretch gently toward the other until the fabric resists. If 10 cm reaches 15 cm, the stretch is 50%; if it reaches 13 cm, it is 30%.
Then let go. Good jersey springs straight back to 10 cm. Fabric that stays stretched has poor recovery and will bag at the elbows and the neckline after a few wears.
How should you set up your machine for jersey?
| Setting | Use | Why |
|---|---|---|
| Needle | Ballpoint 80/12, or stretch 75/11 for fabric with elastane | The rounded point slips between loops instead of piercing them, which prevents skipped stitches and holes |
| Thread | All-purpose polyester | Strong, with a little give |
| Seam stitch | Narrow zigzag (width 0.5–1 mm, length 2.5–3 mm) or the lightning-bolt stretch stitch | Stretches with the fabric so seams do not pop |
| Hem stitch | Twin needle 4.0 mm, or a zigzag 2.5–3 mm wide | Looks like a bought hem and stays stretchy |
| Presser foot | Lower the pressure if your machine allows it, or use a walking foot | Stops the top layer being pushed ahead of the bottom one |
You do not need a serger. It is faster and gives a professional inside, but every seam of a T-shirt can be sewn on a regular machine. The guide to sewing knits on a regular sewing machine shows each stitch close up.
Why are my jersey seams wavy, and how do I fix them?
Rippled seams are the most common jersey frustration, and they almost always have one of these causes:
- You are pulling the fabric. Guide it with your fingertips and let the feed dogs do the moving. Pulling stretches the fabric as it is stitched, and it stays stretched.
- The stitch is too short. A short, dense stitch packs extra thread into the seam and stretches it. Lengthen it to 3 mm.
- The presser foot pushes the top layer. Reduce the pressure or use a walking foot.
- The pieces are cut off grain. Cut knits with the lengthwise ribs (the fine columns on the right side) parallel to the grainline.
- The hem is not stabilized. Fuse a strip of lightweight knit fusible tape, 1.5–2 cm (5/8–3/4 in) wide, inside the hem allowance before folding it up.
If a finished cotton seam ripples, hold a steam iron a little above it and pat it flat: the fibers often shrink back. Viscose and polyester knits recover less, so prevention matters more with them.
How do you get a flat T-shirt neckband?
The neckband is cut shorter than the neckline so that it pulls the edge flat against the body. A common rule is 85% of the neckline length for jersey and around 80% for rib knit, which stretches more.
Fold the band in half lengthwise, divide both the band and the neckline into quarters with pins or clips, and match the quarters. Sew with the band on top so you can see it, stretching only the band (not the shirt) evenly between the marks. Press the seam allowance toward the body, then topstitch if you like.
How do you stop shoulders and hems from stretching?
Shoulder seams carry the weight of the whole garment and grow over time, so sew a strip of clear elastic or stay tape into each one. For hems, the fusible tape mentioned above plus a twin needle gives a result that looks shop-bought.
If the twin needle creates a raised ridge between its two rows (called tunneling), loosen the top tension slightly, lengthen the stitch, or wind the bobbin with a textured nylon thread, which stretches and lets the fabric lie flat.
What should you sew first in jersey?
A T-shirt is the classic first knit project: its seams are short and mostly straight, and it is finished in an afternoon. Sewly's T-shirt pattern uses 1 cm (3/8 in) seam allowances and a 2 cm (3/4 in) hem allowance by default, with the neckband length already calculated for jersey, and its sewing guide gives the steps for the neckline and sleeves you chose. For a complete walkthrough, follow the post on sewing your first T-shirt that fits.