The one setting that matters
Every print dialog has a scaling choice, and most default to shrinking the page so that it fits inside the printer’s margins. That is fine for a letter and wrong for anything measured: graph paper squares, rulers, templates and charts all come out a few percent small. The fix is the same everywhere: find the scaling option and choose Actual size, 100% or None.
Our sheets help by keeping a margin inside the printable area, so there is nothing for the printer to shrink away, and by setting the page size to the paper you chose. If your dialog shows a preview, the sheet should fill the page with a thin white border all round.
Where the setting lives
Windows, Chrome or Edge: in the print dialog open More settings and set Scale to Default or 100. Windows, a PDF viewer: under Page Sizing choose Actual size. Mac: in the print dialog, show details, set Scale to 100% and untick Scale to fit. iPhone or iPad: the Safari print sheet scales by itself; save as a PDF first (share, then Print, then pinch out on the preview and share again as a PDF), open it in Files and print from there with scaling off. Android: save as a PDF through the browser’s print menu, then print the PDF from Files, where the print service lets you choose 100%.
Checking the result
Measure something you know. On graph paper with 5 mm squares, twenty squares should span 100 mm. On the printable ruler, a payment, library or store card should fit the dashed box exactly: cards are made to 85.60 × 53.98 mm by international standard, so they are the one measuring instrument everyone owns. If the card is larger than the box, the page was shrunk; if smaller, enlarged.
A small, steady error, under half a millimetre over 15 cm, is normal: paper is not cut perfectly and takes up a little ink. A larger error is scaling and can be fixed.
Paper size mismatches
A4 and US Letter are close but not the same: A4 is 6 mm narrower and 18 mm taller. If a sheet drawn for A4 goes to a printer loaded with Letter, a careful printer prints it at true size and crops the bottom; a helpful one shrinks it to fit. Choose the paper size you actually have in the maker, and the same size in the print dialog, and neither happens.
Saving a PDF that stays true
Choosing Save as PDF in the print dialog makes a file at the exact page size, with the drawing at true size inside it. That PDF can be printed later, sent to a print shop or opened on a tablet, and as long as whoever prints it chooses Actual size, the result is still exact. If you will print many copies, make the PDF once and print from it rather than from the browser each time.
When true size is not the point
If you only need lines to write on, scaling does no harm; a lined page that is 4% smaller is still a lined page. Actual size matters for rulers, for grids you will measure against, for templates you will cut round and for charts that children compare with physical objects. For those, check once with the card box and your printer is set for every sheet after.