What this measures
Printable ring size chart. Someone searching for this wants a size they can order, and a reason to trust it. A table you can print after the card bar proves the page was not scaled. The phrase people type is “printable ring size chart”, and the text below stays with that job.
Worked example from this one chart: US 8 · UK P · EU 57 · 18.13 mm · 57 mm. If your measurement sits more than about 0.2 mm away from that diameter, you are between sizes. Keep the millimetre. A shop label is a nickname for it, and this page is not a jeweler’s last word when the band cannot be cut later.
Print at 100 percent. Fit-to-page, shrink-to-fit, and a PDF reader’s “scale to paper” will make every circle a lie. Before you trust a printed sizer, the black bar marked 85.6 millimetres must match the long edge of a bank card. If it is short or long, the printer scaled the page. Fix the scale and print again. A screen circle that you already matched to a card is the safer check when the printer will not behave.
How to use it
A ring size is the inside of the band. It is not the outside of the metal and it is not the stone. Jewelers write that inside as a diameter, a circumference, or a shop label. US sizes step in halves. UK sizes use letters. European and Japanese sizes are the inner circumference in millimetres, rounded to a whole number. They describe the same circle, but the labels do not land on the same line. When a conversion falls between two sizes, the honest answer is the millimetre you measured, not a forced whole number.
The circle on this site is only as true as the match you make first. A bank card’s long edge is 85.6 millimetres, the ID-1 size used for credit cards and most identity cards. A ruler’s 100 millimetre span is the other reference. You slide the drawing until it covers the real object, and the page remembers how many pixels make one millimetre on this screen, at this zoom, today. Change the zoom, the text size, or the display scaling and that memory is wrong. Match it again. Typing a number you already measured does not need this step. The hole, the finger lines, and the strip do.
Measure at the end of the day, when the hand is warm. A cold finger is smaller. A workout, a hot bath, or a salty meal makes it larger. Measure the finger that will wear the ring. The two ring fingers are often half a size apart, and the dominant hand is often the larger one. The ring has to pass the knuckle. If the knuckle is much wider than the base of the finger, size for the knuckle and ask for a comfort fit or a sizing bead so the band does not spin once it is on.
What it cannot promise
Width changes the feel even when the inside diameter is the same. A 2 millimetre band and an 8 millimetre band are not the same size in the hand. The wide one covers more skin and feels tighter. Many people go up about a quarter to a half size once the band passes 6 millimetres, and a full size is sometimes right past 8. That is a start, not a rule. A split shank, a tapered band, or a ring that cannot be cut later should be tried on before anyone orders it.
A photo without a known object in the same plane as the ring will lie. A wide lens, a tilted card, and a shadow all change the scale. A partner’s height, glove size, or a borrowed guess is a conversation, not an order. If you land between two sizes, the larger one is usually kinder for a comfort fit, and the smaller one can be right when the band is very thin and the knuckle is narrow. A plain band can often be sized later. An eternity setting, a tension setting, and some alternative metals cannot.
The chart here is one consistent table, not a stack of unrelated national lists. Diameter follows the common US progression of about 0.4 millimetres per half size. Circumference is that diameter times pi. The EU and Japan columns are that circumference rounded to a millimetre. UK letters are the nearest letter shops usually print, and some shops insert a half letter where this table shows one letter. If a maker’s own chart disagrees by a few tenths, trust the millimetre, then ask which of their sizes that millimetre falls into.
Questions
Order with both labels. Write the shop size and the inside diameter in millimetres. If the maker answers with a different half size, ask which millimetre they are using, not which nickname. Measure twice, with the same method, at the same time of day. If the two readings disagree by more than half a size, the string was pulled or the screen match slipped. Match the card again before you pay.
The two ring fingers are often not the same, and the hand you use more is often the larger one. Measure the finger that will wear the ring. A return policy is part of the size. If the shop will not resize and will not take the ring back, the measurement has to be finished before the order, not after the box arrives.