Check your printer
Do this once per printer. Print the check sheet at 100% and measure the bar. If it’s 100 mm, every card you make from now on comes out the right size.
This tool’s whole job is to make a pattern exactly the right physical size for a particular pair of eyes at a particular distance. The file we give you is exact. The one thing we can’t see is your print dialog — and by default it often shrinks the page a few percent to fit a margin it assumes you need. That silently undoes the sizing.
So: check once, here, with a ruler. It takes two minutes and you never have to think about it again.
How to do it
- Download the check sheet for your paper size (above). It’s made in your browser — nothing is uploaded, and it works offline.
- Print it with scaling off. In the print dialog choose“Actual size” / “100%” / “Custom scale: 100”. Never “Fit to page”, “Shrink oversized pages” or “Scale to fit”.
- Measure the black 100 mm bar end to end with a ruler. A ruler graded in millimetres is ideal.
- 100 mm (within about ±0.5 mm) means you’re good. Spot-check the 4 inch bar too — it should read 101.6 mm.
If it measures short (a very common ~96% or ~94%), it is almost always the print dialog, not the file. Turn off “Fit to page”, set the scale to exactly 100%, and print again. Some drivers also have a “borderless” or “page scaling” option worth checking.
If it still won’t print true, note the measured length and your printer model. A printer that reliably prints, say, 96 mm instead of 100 mm is scaling by a fixed factor, and you can compensate by setting your print dialog’s custom scale to the inverse — but fixing the setting is always better than compensating for it.
What’s on the sheet
- A 100 mm bar — the main measurable.
- A 4 inch bar (101.6 mm), as a cross-check in imperial.
- Centimetre and inch rulers, so you can check the whole span, not just two ends.
The bars are drawn as filled shapes whose edges sit exactly on the measurement, and the PDF’s page box is set to the true sheet size in points (A4 → 595.28 × 841.89 pt; US Letter → exactly 612 × 792 pt). Both are checked by automated tests on every build.
Why the cards themselves don’t carry a bar
They can — there’s a “Show 100 mm scale bar” switch in the generator’s Advanced settings. It’s off by default because a printed card works by giving the eye one clear, bold thing to find, and a ruler in the corner is a second thing competing for that attention. Scale is a property of your printer, not of each card, so it’s better checked once — here — than re-proved on every sheet.
Multi-sheet (tiled) posters are the exception: their assembly-instructions page always carries a 100 mm bar, because that’s the page you measure before trimming a dozen sheets.