Why printed ring sizers come out wrong

The sizer looks perfect. The numbers are crisp, the strip is the right shape, and it is four per cent too small. Here is how that happens and how to catch it.

Published 2026-10-23

A printed ring sizer is a measuring instrument made of paper. Everything it tells you depends on one assumption: that the sheet came out of the printer at exactly the size it was drawn. That assumption is wrong surprisingly often, and nothing about the printed page gives it away.

What the printer does to your page

Every printer has an unprintable margin — a few millimetres round the edge where the rollers grip and the head cannot reach. When a PDF is drawn right out to the paper edge, print dialogs offer to shrink it so nothing is lost. Helpful for a photo. Ruinous for a ruler.

• "Fit to printable area" in Chrome and Edge typically scales to 94–97 %.
• "Shrink oversized pages" in Adobe Acrobat Reader does the same, and it is on by default.
• "Shrink to fit page width" in Firefox is on by default too.
• A4 content on Letter paper, or the reverse, triggers an automatic rescale in most dialogs — Letter is 6 mm wider and 18 mm shorter than A4.
• Phone print dialogs frequently scale with no setting exposed at all.

What a few per cent costs you

Here is the whole problem in one table. A finger that is genuinely US 7 — 54.4 mm round — measured on sheets printed at different scales:

The sizer is not broken. It is simply a different size from the one it was drawn at.

Four per cent is the normal amount of shrink, and it is a size and a half. Order that and the ring will not go past the knuckle.

Worse: the error is in the generous direction only when the print is too large. A too-small print makes you order a too-small ring, which is the expensive failure — a ring that cannot be worn at all, versus one that is slightly loose.

The two checks that take ten seconds

A 50 mm line and a real ruler

Every sheet of our printable sizer carries a 50 mm line with ticks every 5 mm. Put a ruler on it. If it reads 48 mm, the sheet printed at 96 % — fix the setting and print again. Do not try to correct for it in your head.

A bank card

The second check needs no ruler at all. Every payment card, ID card, driving licence and loyalty card in the world is made to ISO/IEC 7810 ID-1: 85.6 × 53.98 mm, with a tolerance far below what you could see. Our sheets carry an outline at exactly that size. Lay a card on it. It must sit inside the lines with no white showing and no overhang.

The card check is the better of the two, because almost nobody owns a ruler they trust and everybody owns a card. It also catches the case where a printer scales differently in the two directions, which does happen on worn rollers.

Settings that print at 100 %

Also make sure the paper loaded matches the size you chose in the PDF: A4 content on Letter paper is rescaled automatically by most dialogs.

Other things that make a paper sizer lie

• Thick card stock feeds slightly differently on some printers and can stretch the image along the feed direction. Check the 50 mm line again whenever you change paper.
• Cutting wide of the line. The strip is marked from the slot. Cut the slot in the wrong place and every reading moves by the same amount.
• Pulling the paper tight. Paper does not stretch much, but a damp strip does. Snug, not tight.
• Reading the wrong edge of the slot. The arrow marks the reading edge; use it.
• Reusing a strip. A strip that has been wrapped and pulled a few times softens and lengthens slightly. Cut a fresh one — that is why the sheet has six.

How accurate can a paper sizer be?

With the scale verified, a paper strip reads to about half a millimetre, which is under a quarter of a US size. That is as good as the plastic sizers jewellers give away, and better than a string measurement. It is not as good as a steel mandrel, which is why any ring that [cannot be resized](/blog/ring-resizing/) still deserves a trip to a shop.

If you cannot print at all, the paper strip and ruler method sidesteps the whole problem: you measure with a ruler you can check, rather than with a printed scale you cannot.

What we do about it

Three things, all visible on the sheets themselves. Every page carries the 50 mm line and the card outline, not just the first. The instruction to print at Actual size is printed on the page, not only on the website, because the sheet often reaches a different person from the one who downloaded it. And the layout is drawn in millimetres and converted to points once, at the moment of drawing, so the drawing and the measurements can never drift apart in our own code.

The rest is up to the print dialog — which is why the checks are there.