Embroidery stitch density explained: row spacing, settings and a fabric chart

Software doesn't all show density the same way, which is why the same design can be described as 0.4 mm, 4.0 or 4 pt.

• Millimetres: the direct distance between rows. 0.40 mm means two neighbouring rows sit four tenths of a millimetre apart.
• Points: many commercial packages, and the habits of people who learned on Tajima-format workflows and Wilcom software, express spacing in points, where 1 point is 0.1 mm. So 4 pt is 0.4 mm, 3.5 pt is 0.35 mm and 4.5 pt is 0.45 mm. Embird, for example, describes its density value as the distance between stitches in tenths of a millimetre, so a value of 4 means 0.4 mm.
• Percentages: some programs show density as a percentage of the default spacing. In that case 200% means double the spacing, so half the density.
• Lines per inch or stitches per area: older or hobby software sometimes uses these. Convert them to mm before comparing with other advice.

One detail matters when you measure a tatami fill on screen: each pass across a shape is followed by a pass back, and Wilcom notes that spacing is measured from the end of the row or between every second line. If you count every visible line as a row, you will read the spacing as half of what it really is.

When a thread company recommends a "density of 3.5" for a fine thread, it is using the points scale: 3.5 means 0.35 mm.

Satin columns use the same idea, the spacing between neighbouring zigzag stitches, but the right value depends on the column width.

• Narrow satin (about 1–2 mm wide, small text, thin outlines): can be slightly more open than a fill. Stitches that are only 1 mm long and packed at 0.3 mm look heavy, pile up and cut the fabric.
• Medium satin (2–5 mm, typical lettering and borders): around 0.4 mm is a sensible start.
• Wide satin (above 5 mm): needs tighter spacing so the long stitches cover, plus a solid underlay. Above about 7–8 mm, long satin stitches can snag and loosen, and most digitizers switch to a fill or split the satin.

This is why programs offer automatic satin spacing that changes with column width. Wilcom's example: with 0.4 mm spacing on a 4 mm column, setting auto spacing to 90% closes it to 0.36 mm. Lower percentages tighten the spacing and higher ones open it.

Inside curves need attention too. On a curved satin column, the inside edge is shorter than the outside edge, so the stitches bunch there. Too many bunched stitches on the inside of a curve look poor and are a common cause of thread breaks. Good digitizing software reduces or shortens stitches on the inner edge.

Stitch count rises fast as spacing gets tighter, because every row you add has to be sewn across the whole shape.

As a rough rule, a tatami fill at 0.4 mm row spacing with a normal 3.5–4 mm stitch length puts about 70 stitches into each square centimetre, before underlay. A fully filled 100 × 100 mm (4 × 4 in) square is 100 cm², so that's roughly 7,000 stitches for the top layer alone, and often 8,000–10,000 once underlay, travel runs and borders are added.

Change the spacing and the count changes in proportion:

• 0.30 mm instead of 0.40 mm: about 33% more stitches in the fill.
• 0.45 mm instead of 0.40 mm: about 11% fewer.
• 0.60 mm: about one third fewer, and the fabric starts to show.

Stitch count is more than a number on the screen. It is sew time, thread use and needle penetrations. Every extra row is another set of holes in the same small area of fabric, and that's where most density problems start. If two versions of a design look the same on screen, the one with the lower stitch count is usually the one that sews better.

Most density problems are visible after one test sew-out, if you know what to look for.

Signs a design is too dense:

• It feels stiff and board-like, the so-called bulletproof patch, especially on a T-shirt where it should drape.
• Puckering or tunnelling around the design, even with the right stabilizer.
• Frequent thread breaks, shredding or looping, often in the same area of the design.
• Broken or deflected needles, particularly where a fill overlaps a satin border or another fill.
• Holes or cuts along the edges, because the needle perforates the fabric along a line.
• Raised, lumpy build-up where colours overlap.

Signs a design is too light:

• Fabric colour shows between the rows, most visible with light thread on dark fabric.
• Rows look like separate lines rather than a smooth surface.
• Edges look ragged because the satin border has nothing solid to sit on.
• On towels and fleece, stitches sink into the pile and disappear.

If a fill is too dense, open the spacing by 0.05 mm at a time, check the underlay isn't doubling the coverage, and reduce overlap between neighbouring areas. If it is too light, first check the thread colour against the fabric: a dark fabric under pale thread needs more coverage than the same thread on a matching fabric. Then tighten in small steps, or add underlay before you tighten the top layer.

Fabric is the main reason one density doesn't fit every job. Wilcom's general rule for its fabric presets is that spacing is loosened on thick or dense fabrics and tightened on sheer or open weaves, while stretch knits get more pull compensation, extra zigzag underlay and slightly reduced density.

The chart below is a starting point for 40 wt polyester or rayon thread with a suitable stabilizer. Test on a scrap of the real fabric before a production run.

Use the same chart in points by multiplying by 10: 0.40 mm is 4.0 pt. Satin text on any fabric generally sits between 0.35 and 0.45 mm, adjusted for column width.

Underlay and thread weight change how dense a fill looks without changing its spacing value, so they need to be set together.

Underlay. A layer of running, edge-walk or zigzag stitches sewn first holds the fabric down, lifts the top layer and adds coverage. With a good underlay you can often run the top fill at 0.42–0.45 mm and still get full coverage, which is lighter and softer than 0.35 mm without underlay. Two things to watch:

• Heavy underlay plus tight top spacing doubles up and makes a stiff, bulletproof result.
• Open decorative fills (0.6 mm and above) usually need underlay turned off, because Wilcom notes that underlay and travel runs show through wide spacing.

Thread weight. The higher the weight number, the thinner the thread. Most embroidery advice, including the 0.4 mm standard, assumes 40 wt. A 60 wt thread covers less per stitch, so it needs tighter spacing to hide the fabric: Madeira gives an average digitizing density of 3.5 (0.35 mm) for its Classic Rayon No. 60, with a 65/9 or 70/10 needle. In practice 60 wt is used for small lettering and fine details rather than large fills, because a big area at 0.35 mm takes a long time to sew. Heavier 30 wt thread goes the other way and can run more open than 0.4 mm.

If you switch a 40 wt design to 60 wt thread without changing the spacing, expect the fabric to show through.

A finished stitch file (PES, DST, JEF, EXP) is a list of needle positions, not shapes. When most machines and basic programs scale it, they move every stitch proportionally and keep the same number of stitches.

• Shrinking: the same stitch count lands in a smaller area. At 80% size, a fill that was 0.40 mm becomes 0.32 mm, and satin stitches get shorter. Shrink further and you get the too-dense symptoms above: stiffness, thread breaks and very short stitches that bunch up.
• Enlarging: the rows spread apart. At 120%, 0.40 mm becomes 0.48 mm and stitches get longer. Go further and fabric shows through, and long satin stitches start to snag.

That's why digitizers commonly treat about 10–20% up or down as the safe range for scaling a stitch file without recalculating it. Beyond about ±20%, use software that recalculates stitches and spacing for the new size, or go back to the original artwork and generate the design at the size you need. Embird's resize tool, for example, lets you re-fill areas and set column and fill density when you resize, and you can compare the new stitch count with the original to check the result.

In StitchMyPic, changing the size happens before the stitches are generated, so the row spacing you choose stays the same at 70 mm or 250 mm. You can also re-download the same design at another size during the 7 days after unlocking it, instead of scaling a finished file on the machine.

If you only remember one set of numbers, use these for 40 wt thread and adjust after a test sew-out:

1. Standard fill: 0.40 mm (4 pt). Lighter for knits (0.42–0.45 mm), lighter still for denim and leather.
2. Dense fill for maximum coverage: 0.30–0.35 mm, only on stable fabric and small areas, or for 60 wt thread.
3. Light fill for soft results: 0.45–0.50 mm with a good underlay.
4. Satin text and borders: 0.35–0.45 mm, tighter for wide columns, more open for very narrow ones.
5. Resizing a finished file: stay within about ±20%, and check the stitch count.

In StitchMyPic the density control runs from 0.25 to 1 mm, with quick choices Light (0.45), Balanced (0.40) and Dense (0.30). The fabric presets set density, pull compensation and underlay together: the Knit preset uses 0.42 mm with 0.3 mm pull compensation, Towel / fleece / plush uses 0.38 mm, Denim / heavy canvas 0.45 mm, and Leather / vinyl 0.55 mm without underlay. The free preview shows the stitch count and sew-time estimate, so you can see what a 0.05 mm change does before you sew anything.