Pattern Scaling Calculator
Fix a print-at-home pattern that printed wrong.
Calculate the print scale percentage to correct a PDF sewing pattern whose test square did not print at the right size.
Reprint at this scale
102.6%
currently 2.56% out
Before reprinting, check that 'fit to page' and 'shrink oversized pages' are off — they are on by default in most print dialogues and silently rescale, which is the usual cause rather than the printer itself.
How the Pattern Scaling Calculator works
Every print-at-home pattern carries a test square, and if it measures wrong then every piece is wrong by the same proportion. The fix is to reprint at a corrected percentage rather than to adjust the pieces — a two percent scaling error is a full inch across a forty inch garment, which is most of a size.
Also known as: PDF pattern scale calculator · test square calculator
One square governs everything
A print-at-home pattern carries a test square precisely so this can be checked. If the square prints at the wrong size, every line on every page is out by the same proportion, and no amount of careful cutting recovers it.
The correction is a print percentage: the size the square should be, divided by the size it printed. A square that should be 4 inches printing at 3.9 needs 4 ÷ 3.9, or 102.6%.
The usual cause is not the printer but the dialogue. 'Fit to page' and 'shrink oversized pages' are on by default in most print software and silently rescale, and turning them off is a separate action from setting 100%.
A worked example
A test square measuring 3.9 inches instead of 4 is 2.5% small. On a garment with a 40 inch finished bust that is a full inch missing — most of a size, distributed invisibly across every seam.
Reprinting at 102.6% fixes every piece at once. Adjusting the pieces instead means finding and correcting the same 2.5% in a dozen places, and getting one of them wrong.
Where the answer misleads
Measure across the largest dimension available, and precisely. A 1 inch test square measured to the nearest sixteenth is a 6% measurement error; a 10 cm square measured to the nearest millimetre is 1%. Some patterns provide both — use the larger.
Printers are also not always uniform. A small number stretch slightly in one axis, so checking a square rather than a line is worth doing; if the two dimensions disagree, no single scale percentage fixes it and the pattern needs printing elsewhere.
Finally, under about half a percent is within normal tolerance and not worth chasing. Reprinting a whole pattern to correct 0.3% costs paper and time and gains a fifth of a millimetre per piece.
Frequently asked questions
My test square is too small. What percentage should I print at?
Divide the size it should be by the size it printed. A square that should be 4 inches printing at 3.9 needs 4 ÷ 3.9, or about 102.6%. Set that in the printer dialogue and reprint the test page to confirm.
Why does printing at 100% still come out wrong?
Because 'fit to page' or 'shrink oversized pages' is usually on by default and silently rescales. Turn off any scaling option and set actual size or 100% explicitly — those settings are separate in most print dialogues.
How much error is acceptable?
Under about half a percent is within normal printer tolerance and not worth chasing. Above that, correct it: at two percent, a 40 inch garment is out by 0.8 inches, which is a noticeable fit difference.
Should I measure the square in inches or centimetres?
Whichever the pattern gives, measured as precisely as you can and across the largest dimension available. Measuring a 10 cm square is more accurate than a 1 inch one for the same reason gauge is measured over four inches.