A sewist prints your pattern, measures the test square, and it's 97 mm. Or worse, they don't measure, and cut a whole garment a size too small. Almost every case comes down to one of three things, and each has a clear fix.
What the measurement tells you
| Square measures | Most likely cause |
|---|---|
| 100 mm (± 1 mm) | All good |
| 94–98 mm | The print dialog scaled the page to fit the paper |
| 93.75 mm exactly | Exported at 90 px/in (Inkscape before 0.92) and read at 96 |
| 75 mm | The master was exported at 72 px/in and read at 96 px/in |
| 133 mm | The reverse: exported at 96, read at 72 |
1. "Fit to page" in the print dialog
The most common cause, by far. Most print dialogs offer Fit, Shrink oversized pages or a percentage. Any of them shrinks the page slightly so it fits inside the printer's margins, and a 100 mm square becomes 94–98 mm.
Sewist's fix: choose Actual size or 100%. Print from Adobe Acrobat Reader if the browser's built-in PDF viewer keeps scaling.
Designer's fix: ask the file not to be scaled. A PDF can carry a PrintScaling: None preference that tells the print dialog to default to actual size. Every Sewpress file sets it, and the test square PDF does too.
2. A units mix-up in the master
SVG measures in "user units". Inkscape (since 0.92) and web browsers treat 96 of them as an inch; Illustrator writes SVG at 72 per inch, and Inkscape before 0.92 used 90. Open a 72-per-inch file as if it were 96 and everything shrinks to 75%.
Fix: give the file real units. From Illustrator, save a layered PDF instead of an SVG; from Inkscape, check Document Properties uses millimetres or 96 px per inch. If an upload's test square measures 75 mm or 93.75 mm, Sewpress says so on the inspection screen and rescales with one click, before anything is built.
3. Pages that don't match the paper
A file laid out for A4 printed on US Letter (or the reverse) gets scaled or cropped by the printer. Offer both: Letter is 6 mm wider and 18 mm shorter than A4, so tiles laid out for one don't fit the other.
A checklist for every release
- A 100 mm test square on page 1 of every tiled file, with "print at 100%" next to it.
- Print scaling switched off in every PDF.
- A4 and US Letter tiles, each laid out for its own paper.
- Measure every output before it ships. Sewpress measures each one twice, with two different PDF engines; if it's more than 0.1 mm out, you hear about it before your customers do.
Questions
My square measures 97 mm. Is that close enough?
No: 3% across a 100 cm skirt is 3 cm. That size of error almost always means Fit to page was on.
Can a PDF stop the printer from scaling?
It can ask: the PrintScaling setting tells the print dialog to default to actual size. Most viewers respect it, which is why every Sewpress file sets it.
