Printable Ring Sizer
A printable ring sizer gives you true-size circles to lay a ring on and a paper strip to wrap round a finger, so you can find a size with nothing but a printer and a ruler. Each circle is drawn at the exact inner diameter of its US size, from 3 (14.1 mm) to 15 (23.8 mm), and a bank-card box checks that the print came out at 100%.
The sheet
How is the sheet drawn?
Circle diameter = 11.63 + 0.8128 × US size, in mm. Strip marks sit at each size’s circumference, π × that diameter. The sheet is an SVG whose units are millimetres, on a page set to A4, so a print at 100% is at true size.
Worked example. The US 7 circle is 11.63 + 0.8128 × 7 = 17.32 mm across. On the strip, the US 7 mark is at π × 17.32 = 54.4 mm. The card box is 85.60 × 53.98 mm, the size of every payment card, so a card that fits it proves the scale.
Circles or strip?
Use the circles when you have a ring that fits; they are more accurate, because a ring is rigid and the match is visible. Use the strip when you are measuring a finger; it gives a circumference you can type into any of the tools. Paper stretches a little when pulled, so wrap the strip snug but not tight.
Checking a print
Any payment, library or store card fits the dashed box when the print is true, because all of them are made to the same international size. A card that overhangs the box means the page was shrunk; one that falls short means it was enlarged. Our chart page and on-screen sizer use the same card as their reference.
Keeping it
Printed on card and kept in a drawer, the circles are a ring gauge for life. Mark the sizes of the people you buy for on it, with the date, since fingers change.
Questions about the printable sizer
How do I print it at the right size?
In the print dialog choose Actual size or 100%, never “Fit to page”. Then lay any bank card on the dashed box: if the card fits the box exactly, the circles and the strip are at true size. If not, the printer scaled the page; turn scaling off and print again.
How do I use the circles?
Lay a ring that fits on the circles until you find the one that just fills the inside of the band, with no white showing between the printed line and the metal. The number inside the circle is the US size; the line under it gives the UK and EU sizes.
How do I use the strip?
Cut it out along the border, wrap it round the base of the finger with the 0 end on top, and read the mark where the end meets the scale: the millimetres are your circumference and the blue marks show the US size. Type the millimetres into the measuring page for every scale.
Why are the circles slightly different from another site’s printable?
Because many printables are made at approximate sizes or scaled by the browser. Ours are drawn at the exact inner diameter of each US size (11.63 + 0.8128 × size mm) on a page set to A4, and the card box lets you prove the print is true.
Can I print on Letter paper?
Yes. The sheet is A4 (210 × 297 mm); on Letter (216 × 279 mm) the bottom 18 mm is cropped, which is blank, so nothing on the sheet is lost, as long as the print is at 100% and not shrunk to fit.