Density is the single most-asked-about embroidery measurement. The honest answer is 'it depends on the fabric' — and roughly speaking, here are the ranges that work without puckering, needle damage, or thread breakage. Numbers below are for solid fills; satin columns behave differently (see the long-satin article).
Density × fill type
The same numerical density behaves differently depending on the fill pattern. Tatami fill (parallel rows with offset turn-points) absorbs density gracefully — the offset prevents the stitches from accumulating in one fabric coordinate. Satin stitch (parallel back-and-forth columns) puts every stitch perpendicular to the column axis; equivalent density on a satin will perforate fabric a tatami fill at the same density wouldn't.
- Tatami fill: the table above applies directly.
- Satin column: derate the upper end by ~20% for tightly-woven fabrics, ~30% for knits.
- Run stitch outlines: density is determined by stitch length (typically 2-4 mm) — the per-area numbers don't apply.
- Cross-hatch and decorative fills: each pattern has its own tolerance; consult the fill's documentation.
What ValidStitch checks
ValidStitch's density check looks at per-region stitch density against the fabric profile set on the project. The default thresholds match the table above; you can adjust per project for designs at the edge. The validator surfaces the exact regions over threshold with the percentage they're over — handy when the design as a whole is in range but one logo area is too dense.