Usually slightly looser than your normal setting, because topstitch thread is thicker and the same dial number grips it harder. But test rather than assume — topstitching is visible, and an unpicked line shows on the fabric.
Set the length first. Topstitching wants 3 to 3.5 mm. A long stitch is what makes a topstitched line read as deliberate rather than as ordinary construction sewing on show.
Use a topstitch needle with heavy thread. It has a larger eye and a deeper groove, which stops the thread shredding as it passes through.
Then adjust the tension. Sew on a scrap made up of the same number of layers as the real seam, including any interfacing. Thick thread on top with ordinary thread in the bobbin often looks right only after loosening the top tension by half a number or a whole one.
Ordinary thread in the bobbin is normal here. Heavy thread top and bottom overloads the bobbin case and rarely improves the result.
Slow down. Topstitch thread carries more load, and speed is where it snaps.
Two things that matter more than tension. A guide, so the line stays parallel — the edge of the foot, a seam guide, or a strip of tape on the bed. And not stopping mid line, because every restart shows.
If the line looks lumpy rather than uneven, the fault is the needle or the thread path, not the setting.
Questions people actually ask
Can I topstitch with ordinary thread?
Yes, and two parallel lines close together give a similar weight without heavy thread. It is a common alternative.
My topstitching wanders.
Use a physical guide rather than your eye, and sew slowly. Topstitching is judged on straightness above everything else.
Last reviewed 2026-08-11