Definition
A test square is a square of known size printed on a PDF sewing pattern, measured after printing to confirm the pages printed at true scale.
Printers and PDF readers often shrink pages slightly to fit their margins, and a pattern printed at 97% is 3% too small in every direction: on a 100 cm (39 1/2 in) hip, that is 3 cm (1 1/4 in) less room. The test square catches this before you cut and tape anything.
How to use it:
- In the print dialog, choose actual size, 100% or no scaling. Turn off options such as fit to page or shrink oversized pages.
- Print the page with the test square first, on its own.
- Measure the square with a ruler in both directions. It should be exact to within about 1 mm (1/32 in).
- If it is off, check the scaling setting again, try another PDF reader or check your printer driver, then print the rest.
Measure both sides: some printers scale only one direction, which turns the square into a rectangle and distorts every pattern piece.
Every Sewly PDF includes a test square measuring both 5 cm and 2 in, so you can check in the unit you are used to. The same check applies to copy shop prints and projector calibration. More in how to print a PDF sewing pattern at the right scale and why the test square matters.