Resizing embroidery designs safely: the 20 % rule, density correction, and when to re-digitise

"Resize within 10 %" is the advice on every design shop's page, and it is right for what most software does, which is multiply the coordinates. This guide explains why that limit exists, what density correction changes, and what it cannot change.

What plain scaling does

A stitch file is a list of needle positions. Scaling to 130 % multiplies every position by 1.3 and keeps the list the same length. The design is 30 % wider and taller with exactly the same number of stitches over 1.69 times the area.

For a fill that means rows 0.4 mm apart become 0.52 mm apart, and the fabric shows between them. For a satin column it means the zigzag that put a stitch every 0.2 mm along the column now puts one every 0.26 mm, and the column looks combed. At 80 % the opposite: rows at 0.32 mm, penetrations every 0.16 mm, twice the thread in the same square millimetre in the worst spots, short stitches where there were none, and puckering.

Ten percent either way changes spacing by a tenth, which is inside what fabric and thread absorb. Twenty percent is visible if you know what to look for. Beyond that it is visible to anyone. That is the whole basis of the rule.

What density correction does

The resize tool does not stop at multiplying. It reads every run of stitches between jumps, trims and colour changes, classifies it, and rebuilds it at the original pitch:

• Satin. A satin column is a zigzag: successive stitches reverse direction and stay a steady length. The tool keeps the two rails, which scale with the design, and re-samples the zigzag along them so the same-side spacing stays what the digitiser set (0.4 mm in most commercial files). A 130 % column gets 30 % more zigzags.
• Fill. Rows of short collinear stitches, alternating direction row by row. The tool interpolates new rows between the existing ones (or drops rows when shrinking) to keep the original row spacing, and re-splits each row at the original stitch length.
• Running stitch and everything else. Scaled, then re-split so no stitch exceeds the longest stitch the original used.

The report shows density before and after, and what plain scaling would have given, so you can see the correction rather than take it on trust.

Because the classification works on stitch geometry alone, it works on any stitch format we read, and results are best on designs digitised the usual way: satin borders, tatami fills, running details. A design that is all random-fill texture or all running stitch is scaled and re-split but has little to re-space.

What it cannot do

Two things are set at digitising time for one size and one fabric, and they are baked into the stitches.

Underlay is the sparse first layer that anchors the fabric and supports the top stitches. It scales with the design like everything else, and it is re-spaced like everything else, but its type was chosen for the original size. A 20 mm letter digitised with a centre-run underlay is fine; the same letter at 40 mm wants a zigzag underlay under 8 mm columns, and no resizer adds one.

Pull compensation is the extra width added to satin and fills to counter the fabric pulling in. It is an absolute amount, 0.2 to 0.4 mm, not a percentage. At 130 % the compensation is scaled too, so it is 0.26 to 0.52 mm, a little too much; at 70 % it is a little too little. Within about ±20 % the difference is under 0.1 mm and invisible. Past that, satin edges start to look too fat or too thin, and fills begin to show gaps against their borders.

So the corrected limit is not spacing any more; it is these two, and the tool says so in its report when you go past 20 %. The honest answer past about 25 to 30 % is the native object file and a re-export, if the designer has it (why native files matter).

Going smaller

Shrinking has a floor that has nothing to do with density. Satin narrower than about 1.2 mm is a running stitch with ambitions, and details narrower than that vanish. A 4 mm satin at 50 % is 2 mm and fine; a 1.5 mm satin detail at 50 % is 0.75 mm and will not read. Lettering is the usual casualty: 12 mm satin letters at 60 % are 7 mm, near the point where the letter's strokes are thinner than the thread. Re-letter with the lettering tool at the target size instead of shrinking; you get columns designed for that size.

Short stitches appear when shrinking too. The tool re-splits runs so nothing goes under the original minimum, but a design that already had 0.4 mm stitches at 100 % will have 0.28 mm stitches at 70 %, and those break thread. The pre-flight check on the result counts them.

Going larger

Enlarging widens satin columns. Satin over about 7 mm snags on anything that touches it and sinks into soft fabric; over 12 mm the stitches exceed most machines' limits and are written as jumps. The tool warns at both thresholds. A design whose widest satin is 4 mm can go to 170 % before the first warning; a design with 6 mm columns cannot go far at all. The fix for a big enlargement is a fill instead of satin, which is a digitising change.

A procedure

1. Run the original through the pre-flight check. Note the density, the widest satin, the shortest stitches. A design that is already dense or already has short stitches has less room.
2. Resize with correction. Read the before/after table. Look at both previews.
3. If the report warns about satin width past 7 mm or about the ±20 % limit, decide whether the fabric forgives it. Twill and caps forgive a lot; t-shirts forgive little.
4. Check the result fits the hoop; the hoop checker shows the margin.
5. Stitch a test on the same fabric before a paid job. Measure it. If the satin edges are visibly fat or the fill shows gaps at its border, the compensation is out for this size and the job needs the native file.