Embroidery stitch density: what to set, by fabric

Density is the gap between rows of stitching, measured in millimetres, so a smaller number means heavier coverage. It is the single biggest control you have over whether a design sits flat on the fabric or fights it.

0.4 mm is the standard starting point for a fill and for a satin on stable woven fabric. Everything below is a deviation from that, and the direction of the deviation is nearly always looser, not tighter.

By fabric

• Stable woven (cotton, canvas, denim, twill): 0.4 mm. Canvas and drill will take 0.35 mm for a heavier look.
• Fleece, terry, thick knits: 0.45 to 0.5 mm, with a tatami underlay so the fill does not sink into the pile. A water-soluble topping keeps stitches on the surface.
• Stretch knits, jersey, performance fabric: 0.5 mm, zigzag underlay every time, and satins capped at 6 mm wide. Anything heavier distorts as it sews.
• Light woven (silk, lightweight cotton, polyester satin): 0.5 to 0.55 mm, edge-walk underlay only, satins no tighter than 0.5 mm. These pucker fastest.
• Towelling: as fleece but worse. Tatami underlay plus an edge run, a topping, and nothing smaller than 8 mm of lettering.
• Caps: 0.45 mm, satin underlays, and sew outward from the centre seam.

What goes wrong at each end

Too tight (below about 0.3 mm) and the needle is perforating rather than stitching. The symptoms are thread breaks in the same spot every time, a stiff board-like patch, and puckering round the design. It also costs runtime: dropping a large fill from 0.35 to 0.45 mm removes roughly a fifth of its stitches, usually with no visible difference.

Too loose and the fabric shows between the rows, which looks like a mistake on a dark garment under a light thread. The fix is not always more density: a fill in the right direction, or an underlay, often covers better than a tighter one.

Density is not the same as stitch count

Two designs at the same density can differ hugely in stitch count, because count follows area. If a design is too heavy for the fabric, loosening density helps; if it is simply slow to sew, the answer is usually less area or fewer colour changes.