I built a tiny tool that catches the "printed at 94%" problem

Hi everyone,

I built a free print scale checker as part of my printer test site, after running into a frustrating problem: prints that look fine but come out the wrong size.

The usual cause: an A4 file printed on Letter with "Fit to page" on shrinks to about 94%. Nothing looks broken, but templates, labels and patterns are off.

What I focused on:

• Print one sheet, measure a 100 mm bar, type the number
• It tells you the scale and whether it matches a paper-size mismatch
• Runs in the browser, nothing uploaded

What I learned:

• "The printer printed" and "it printed correctly" are different checks
• Real vector PDFs beat HTML print for exact sizes

Question for developers: have you built anything that has to print at an exact size? How did you test it?

Comments

[Mythex]

Two additions that would make the check catch more:

• Print two bars, one across and one down the page. Some printers scale the paper-feed direction slightly differently from the other, so a single horizontal bar can read 100 mm while circles still come out as ovals.
• Expect a second common number besides 94%: around 96-97%, which is what "fit to printable area" gives when the page itself is the right size but the printer's margins shrink it. Browser PDF viewers often default to that, so an "Actual size / Scale 100" reminder next to the download button saves a lot of wasted sheets.

Does the tool tell people which setting to change once it detects the mismatch, or just the scale?