The ruler check: verify a print before you submit it

Every print sheet we render carries a straight black line in its footer with a sentence next to it: this line must measure exactly 50 mm / 2 in when printed; if not, your printer scaled the page. Measuring that line with any household ruler is the only reliable way to know a print is at 100 percent before an examiner measures it for you. This guide explains what the line proves, the arithmetic of a failed check, and what to change when it fails.

What the line proves

The sheet is laid out at 300 DPI, so the software knows exactly how long the ruler line should be on paper: 2 inches on the 4 x 6 and US Letter sheets, 50 millimetres on the A4 and 5 x 7 sheets. Printing scales the whole page uniformly or not at all, so if the line is right, every photo on the sheet is right, and if the line is wrong, every photo is wrong by the same factor. There is no need to measure the photos themselves, which have soft edges that are hard to put a ruler on; the line has crisp ends for exactly this purpose.

The arithmetic of a small error

Scaling errors look harmless and are not. A 50 mm line that measures 48 mm means the page printed at 96 percent, so a 35 x 45 mm photo became 33.6 x 43.2 mm, outside what HM Passport Office will cut down for the UK printed passport, whose head must measure 29 to 34 mm crown to chin on a 45 mm print. Australia's rule is tighter still: the face on an Australian passport photo must span 32 to 36 mm chin to crown, so a head rendered at 33 mm needs only a 4 percent shrink to fall out of range. The same logic catches enlargement: a 52 mm line means the US passport photo is no longer 2 x 2 inches, which is the first thing an acceptance agent checks.

Running the check

Ten seconds with any ruler, at home or at the store counter.

1.Lay the ruler along the printed line, zero at the left tick.
2.Read the right tick: it must sit exactly on 50 mm, or on 2 in for a 4 x 6 or Letter sheet.
3.If it is short, the printer shrank the page: reprint with scaling at 100% and borderless off, as the settings walkthrough shows.
4.If it is long, borderless or 'fill page' mode enlarged the page: turn it off and reprint.
5.At a lab or kiosk, measure before leaving the counter and ask for a reprint 'at 100 percent, no resizing' if it fails; a lab printing the Canadian passport photo must also print it on photographic paper, since Canada refuses home prints entirely.

When the line is right but the photo still fails

A correct ruler proves the print size, nothing more. If the head is the wrong size on a correctly printed sheet, the problem happened at capture, not at the printer: the crop put the head outside the authority's band. Our checklist shows the measured head height against each country's range before you pay, and the head size guide lists the bands country by country.

Frequently asked questions

My ruler shows 49 mm. Is that close enough?

That is a 2 percent shrink, which puts a 35 x 45 mm photo at about 34.3 x 44.1 mm. Authorities publish target sizes, not printing tolerances, so there is no official 'close enough'; a reprint costs less than a rejection.

Do store machines really scale prints?

They can: kiosk 'fit' options and borderless modes behave exactly like home-printer scaling. That is why the check is worth doing at the counter, where a reprint takes a minute.