Setup
Tension & stitch length
Two dials decide what your stitches actually look like. Learn what each one does, how to read a balanced stitch, and how to test on scrap before you commit to your project fabric.
If threading is a yes-or-no question, tension is a how-much question. There's no single "correct" setting — the right tension depends on your thread, your fabric, and the stitch you're sewing. The good news is that there are only two dials, and you can test both on a fabric scrap in under a minute.
The tension dial
The tension dial — usually a numbered knob on the front of the machine, typically reading 0 to 9 — controls how tightly the tension discs squeeze the top thread as it passes through them. Higher numbers = tighter squeeze = the top thread gets pulled less easily, which means more top thread is held back when the stitch forms.
There's also a bobbin tension, set by a tiny screw on the bobbin case. Leave it alone for now. Adjust bobbin tension only if top-tension adjustments don't fix the problem — and even then, only by quarter-turns.
What a balanced stitch looks like
A balanced stitch interlocks the top thread and bobbin thread inside the fabric, in the middle of its thickness. From either side, you should see clean stitches with no loops, no thread tails sneaking through.
- Top tension too tight: the top thread pulls the bobbin thread up through the fabric. You'll see little bumps or dots of bobbin-color on the top side.
- Top tension too loose: the bobbin thread pulls the top thread down. You'll see loops of top-color on the bottom side.
If your top thread and bobbin thread are different colors, this gets immediately obvious. When testing, deliberately use contrasting thread colors — it'll save you ten minutes of squinting.
Default starting point
For most all-purpose polyester thread on medium-weight cotton or linen, start at about 4 on the top tension. Most machines come from the factory dialed in this range. From there, adjust by half-numbers.
Stitch length
The stitch-length dial sets how far the fabric feeds between each needle puncture. It's measured in millimeters on most modern machines.
| Length | Use it for |
|---|---|
| 1.5–2.0 mm | Topstitching, reinforced seams, sewing through several thick layers |
| 2.5–3.0 mm | General-purpose sewing — the default for almost everything (start here) |
| 3.5–4.0 mm | Topstitching on thicker fabric, sewing slippery fabric (longer stays put) |
| 4.0–5.0 mm | Basting (loose temporary stitches), gathering, ruffles |
| 0 | The machine sews in place — used at the start/end of a seam to lock it |
The scrap test
Before any project, do this once with the actual thread and fabric you'll be using.
Fold your scrap in two layers. Most sewing happens on two layers (seams join two pieces), so a single layer doesn't test what you'll actually do.
Use contrasting thread colors top and bobbin. Bright pink top with bright blue bobbin works. You're testing visibility, not making it pretty.
Sew a 10 cm line at default tension (4) and stitch length (2.5 mm). Look at the top: do you see bobbin color? Look at the bottom: do you see top color? Either is a sign of imbalance.
Adjust top tension in half-number steps and sew another line right next to the first. Mark each line with the tension value you used (a chalk number works). Keep going until both sides look clean.
Change stitch length last. Once tension is right, try 2.0, 2.5, and 3.0 — pick what looks right for your project.
When stitches look wrong, suspect threading first
Before adjusting the dials, re-thread the machine (top and bobbin). A surprising amount of "tension trouble" is actually a threading slip — a missed guide, the thread not seated in the tension discs, the bobbin loaded backwards. Threading is faster to redo than chasing the dials.