Definition
Stitch length is the distance between two needle holes in a line of machine stitching, set in millimeters on most machines, or in stitches per inch.
Most machines default to 2.5 mm, a good all-round length. Shorter stitches are stronger and more flexible on curves; longer stitches are easier to remove and look bolder on the surface.
| Length | Stitches per inch | Use |
|---|---|---|
| 1.5 mm | 16–17 | Reinforcing corners, crotch curves, collar points |
| 2–2.5 mm | 10–12 | Standard seams; shorter for lightweight fabric |
| 3–3.5 mm | 7–8 | Topstitching, thick fabric, denim |
| 4–5 mm | 5–6 | Basting, gathering, easing |
To convert, divide 25.4 by the length in millimeters: 2.5 mm gives about 10 stitches per inch. American and older patterns often state lengths in stitches per inch (spi).
Fabric matters. Thin silk and voile pucker with long stitches, so drop to 2 mm. Thick denim or canvas can jam with short stitches, so go up to 3 mm or more. On knits, a straight stitch of any length can snap when stretched: use a narrow zigzag stitch or your machine's stretch stitch.
Stitch length is set by how far the feed dogs move the fabric at each stitch. If the stitches come out shorter than the setting, the fabric is being held back: let it feed on its own, or use a walking foot on thick or sticky material.