The mistake that ruins fit most often is letting the printer scale the PDF: "fit to page" or "shrink to printable area" reduces every piece by 2 to 6 %, enough to drop a dress by a full size. Always print at 100 % (actual size), measure the test square on the first page before printing the rest, and match the paper size in the print dialog to the paper in the tray. The other mistakes below, from browser printing to trimming the wrong edge, are smaller on their own but add up to the same result: pieces that do not match your measurements.
What are the symptoms, and what causes them?
| Symptom | Likely cause | Fix |
|---|---|---|
| Test square measures 4.8 cm instead of 5 cm | Scaling set to fit or shrink | Set 100 % or actual size and reprint the first page |
| Test square is right one way and wrong the other | Page stretched by a driver option, or paper fed damp | Turn off any "scale to fit width" option; use dry paper |
| Pages do not line up at the marks | Pages rotated, or trimmed on both edges | Turn off auto-rotate; trim one edge per join only |
| Pieces run off the edge of the page | File is A4 printed on Letter, or the reverse | Download the file for your paper, or set the paper size to match |
| Every size printed | Printed from a browser or a reader without layer support | Open in Acrobat Reader on a computer and hide the sizes |
| Missing pages or pieces | Page range set, or duplex printing | Print all pages, single-sided, and check against the page map |
| Pattern fits the toile but the final garment is small | Pattern printed again later at a different setting | Re-measure the test square on every print, not only the first |
Mistake 1: Letting the printer scale the page
Print drivers want to help. "Fit to page", "shrink oversized pages" and "scale to printable area" all sound harmless and all change the size of your pattern. Most PDF files have margins that fall inside a printer's printable area, so no scaling is needed. Choose "actual size" or "100 %", and if there is a "custom scale" field, make sure it says 100.
How to spot it: the test square is short in both directions by the same amount. The fix: change the setting and reprint the first page. The test square post shows how a 3 % reduction changes a bodice.
Mistake 2: Printing an A4 file on Letter paper, or the reverse
A4 (21 × 29.7 cm) is narrower and taller than US Letter (8.5 × 11 in, 21.6 × 27.9 cm). Print an A4 file on Letter and the bottom 1.8 cm is cut off on every page; print a Letter file on A4 and the sides lose a strip. Printers hide this with scaling, which brings back mistake 1.
How to spot it: a margin of the pattern is missing, or alignment marks on one edge are absent. The fix: download the file made for your paper. A4 vs Letter explains the difference, and a pattern maker that offers both sizes saves you the trouble.
Mistake 3: Printing from a browser or a phone
The PDF preview built into Chrome, Safari and Edge, and most phone apps, ignore layers, apply their own scaling and sometimes add headers and footers. They are fine for reading the instructions and wrong for printing the pattern.
How to spot it: every size prints, or the test square is off even though you chose 100 %. The fix: download the file and open it in Adobe Acrobat Reader or another full desktop reader, then print from there. The printing guide lists the settings screen by screen.
Mistake 4: Checking the test square once, or not at all
Print the first page alone and measure the square with a ruler, not by eye. Measure it in both directions: a square that is 5 cm (2 in) wide and 4.9 cm tall means the page was stretched, which no single scale setting will cause. Then measure it again on a page from the middle of the pattern, since some drivers treat the first page differently from the rest.
Repeat the check every time you print, even a pattern you printed correctly last month. A driver update, a different computer or a different reader can reset the defaults.
Mistake 5: Auto-rotate and center
"Auto-rotate and center" turns a page to match the paper orientation and shifts it to the middle. On a tiled pattern it can rotate alternate pages, so the alignment marks sit on the wrong edges and the overlaps face the wrong way.
How to spot it: some pages look upside down or sideways next to their neighbors, and the marks do not meet. The fix: turn the option off, set the orientation to match the file, portrait for most patterns, and reprint.
Mistake 6: Double-sided printing
Duplex is a sensible default for documents and ruins a tiled pattern, which prints half of the pages on the back of the other half. Set single-sided, and check that the setting is not overridden by a printer preset.
Mistake 7: Trimming both edges, or the wrong one
Tiled pages overlap by a margin, usually about 1 cm (3/8 in). You trim that margin on one edge of each join only, so the trimmed page lies on top of the untrimmed one and the marks meet. Trim both and the pattern loses the width of the margin at every join. Trim neither and you are aligning through paper.
How to spot it: the pattern is right at the test square but short across a piece that spans several pages. The fix: follow the maker's scheme, usually the top and the left edge, or the right edge and the bottom, and nothing else. Assembling a tiled PDF pattern shows the order.
Mistake 8: Aligning the paper edges instead of the marks
Printers do not place the image at exactly the same spot on every sheet. If you tape pages by butting their edges together, a 1 mm offset per page becomes 6 mm (1/4 in) across a trouser leg. Align the marks, the small crosses or triangles printed at the corners and edges, and let the paper edges fall where they will. Overlapping pages on a light table or a window helps.
Mistake 9: Cutting on the wrong line
Some patterns include the seam allowance in the cutting line; some draw only the stitching line and expect you to add it. Cut a no-allowance pattern as is and every seam is 1.5 cm (5/8 in) too far in; add allowance to a pattern that already has it and the garment grows by the same amount at every seam.
How to spot it: the instructions say which it is, and a pattern with allowance usually shows both lines or states "seam allowance included" on the cover. The fix: read the cover before cutting. Sewly, for instance, includes 1.5 cm (5/8 in) on woven fabric and 1 cm (3/8 in) on knits by default and prints the amount on the pattern.
Mistake 10: Letting the paper move after printing
Paper takes up moisture. A pattern left on a damp floor or glued with too much wet glue stick swells, and a taped pattern pressed with a hot iron shrinks and ripples where the tape melts. Store the assembled pattern flat and dry, and never iron tape.
Scaling can also creep in at the copy shop. If you order a large-format print, say "100 %, no scaling" when you order and measure the square at the counter.
How do you check a pattern before cutting fabric?
- Measure the test square on the first page and on one page from the middle, both directions.
- After assembly, measure one long piece against a known dimension, for example a center-back length or a stated finished skirt length minus the hem. Many patterns print a finished length on the piece.
- Walk the seams: lay the front side seam on the back side seam and check they are the same length between notches. A mismatch of more than 2 mm (1/16 in) points to a bad join.
- Check that the notches that should meet across a seam do meet. On a sleeve, the front and back notches should land on the armhole notches.
Five minutes here is cheaper than a toile that lies about the fit. If the pattern passes, the fit problems you find later are fit problems, not printing problems, and how to check your printer scale can go back on the shelf until the next pattern.