Printing accurate scale rulers

A PDF can describe a line exactly 100 mm long, but your print dialog, printer driver and paper all get a say in what comes out. Here's how to get it right and how to check.

Why printed rulers come out wrong

• Fit to page. Many PDF viewers and browsers shrink pages to fit the printable area by default, often to between 94% and 97%. It's the most common cause.
• Paper size mismatch. Printing an A4 file on Letter paper, or the other way round, can trigger automatic scaling. Pick the file for the paper in your printer.
• Printing from a screen. Screenshots and on-screen previews have no reliable physical size, because the operating system doesn't know your monitor's true pixel density.
• Mechanical tolerance. Even at 100%, paper feed and drum speed can stretch or squeeze the image very slightly, usually more along the feed direction.

Settings to use

1. Download the PDF from the ruler generator and open it in a dedicated PDF viewer rather than printing from the browser preview.
2. Set scaling to Actual size, 100% or None. Turn off "Fit", "Shrink oversized pages" and "Auto-rotate and center" if they rescale.
3. Choose landscape and the matching paper size.

Our PDFs set the viewer preference PrintScaling /None, which asks compliant viewers to default to no scaling. Some viewers ignore it, so always check.

How to check a print

Every sheet has three check marks: a 100 mm line, a 4 inch (101.6 mm) line, and an outline matching an ISO/IEC 7810 ID-1 card (85.60 × 53.98 mm, the size of most bank and ID cards). Measure the lines with a steel rule or lay a card on the outline. If the 100 mm line measures 96.5 mm, the print was scaled to 96.5%. Fix the setting rather than compensating.

How accurate can paper be?

We don't publish a single accuracy figure, because it depends on your printer and paper and we haven't tested every combination. In practice, check the 100 mm line yourself. A difference under about half a millimetre usually can't be seen with an ordinary rule. Paper also absorbs moisture and can change size slightly as humidity changes, so for precision work, glue the print to card or laminate it and re-check it now and then.

SVG or PDF?

Use the PDF for printing. Use the SVG when you want to edit the ruler in a vector program, or send it to a laser cutter or plotter. The SVG declares its size in millimetres, so it imports at true size in most vector editors. Check the import dialog for any scaling option.