2.5 mm is the default, and most machines arrive set to it. Everything else is a departure from that for a stated reason.
Ordinary seams on woven fabric — 2.5 mm. Short enough to be strong, long enough not to perforate the cloth.
Fine fabric, silk, lawn, sheers — 2 mm. A long stitch on a fine weave sits proud and puckers.
Curves and pivots — 1.5 to 2 mm. Shorter stitches follow a curve more smoothly and give more control at a corner.
Denim, canvas, fleece — 3 to 3.5 mm. A longer stitch lets the feed dogs take a bigger bite, and it stops a heavy seam turning into a line of perforations.
Topstitching — 3 to 4 mm. Longer reads as deliberate. It is the length as much as the thread that makes topstitching look finished.
Basting and gathering — the longest the machine offers, usually 4 to 5 mm.
Knits — around 2.5 mm on a stretch stitch or a narrow zigzag. The length matters far less than the stitch having some give.
Two mistakes are common. Leaving the machine on one length for a whole project, and trusting the dial rather than a test seam. Some older machines are marked in stitches per inch rather than millimetres, where a bigger number means a shorter stitch — which catches people out.
Test on a doubled scrap of the actual fabric. A sample beats any number printed in a manual.
Questions people actually ask
Does a longer stitch weaken the seam?
Slightly, and it also reduces puckering. On heavy fabric that trade is worth making, because a very short stitch weakens the cloth itself.
My dial has no millimetres.
It is marked in stitches per inch. Roughly ten to twelve per inch is the equivalent of 2.5 mm.
Last reviewed 2026-08-11