Ring size converter

Enter a ring size or an inside measurement to compare the US and UK chart labels, a rounded circumference size, and dimensions in millimetres and inches. The results follow a named chart. They are not a guarantee that a particular ring will fit, and some inputs correspond to more than one chart row. When that happens, the calculator shows the alternatives together instead of silently choosing one.

For the gift itself, start with the wife gift guide or our unique gifts for a wife guide. Check the seller's own sizing instructions before ordering a ring, especially when the purchase is intended as a surprise.

Choose the system on the existing label

Select US, UK, rounded circumference, or the measurement you have. A number such as 6 means very different things as a US label and as a diameter in millimetres. Make sure the dropdown describes the value you are entering. Diameter measures across the inside of the ring; circumference measures around that inside opening.

The underlying chart covers US 3 through 13.5 in quarter-size steps. Its inside diameters run from 14.1 to 22.6 mm and circumferences from 44.3 to 71.0 mm. Inputs outside the selected column's range produce an error. Values between numeric entries return the nearest listed row, with an explicit notice; an exact tie shows both neighbors.

UK half sizes accept forms such as L.5, L½ and L 1/2. Letter case does not matter. Numeric inputs accept a decimal point or comma, and a half-size symbol such as 6½. Use decimal inches when entering an inch measurement. Do not add unit words, scientific notation or a seller's product code to the size field.

Understand where the figures come from

US labels, UK labels and metric measurements use GIA's published international ring chart. The tool preserves its stated precision rather than presenting extra decimals as better measurements. Different publishers can use different letter equivalents; these are the selected chart's associations, not a universal rule for every retailer.

One source cell needs explanation. GIA prints the UK entry beside US 4.75 as 1.5. This tool uses I.5, supported by the House of Lor size guide, and identifies that correction in the result. GIA leaves the UK entry for US 13.25 blank; that output says Not listed. It does not borrow a nearby letter.

The EU-style output is calculated by rounding the listed circumference to the nearest whole millimetre. It is labeled as an approximation, not a transcribed ISO conversion table. ISO 8653:2016 concerns ring measurement and designation using specified equipment; that does not make every international label on an online chart an exact ISO equivalent.

Inch values divide the chart's millimetres by 25.4, the exact conversion documented by NIST. They display four decimal places to make comparisons possible. Those additional digits do not improve the precision of the original chart or of a measurement taken at home.

Compare exact and ambiguous results

US 6 returns UK L, an approximate circumference size of 52, an inside diameter of 16.5 mm and circumference of 51.8 mm. In inches, those measurements display as 0.6496 and 2.0394. UK M returns US 6.5, approximately 53, with 16.9 mm diameter and 53.1 mm circumference.

Entering an approximate circumference size of 54 matches two rows: US 6.75 and US 7. Their UK labels are M.5 and N, and their circumferences are 53.7 and 54.3 mm. Both round to 54. The slash-separated outputs follow the row order in the comparison table below them. A more precise known measurement can help distinguish the entries.

Nearest does not mean recommended. A value halfway between rows is a chart ambiguity, not an instruction to buy the smaller or larger ring. Keep the measurements and the source convention with any size you pass to the seller.

Confirm the fit of the actual ring

Sizing depends on the finger and the ring design as well as the label. GIA's measurement guidance treats standard bands, wide bands, tapered rings and other shapes separately. A size converter cannot examine those differences.

Ask the jeweler to confirm the intended finger and model. This tool does not measure a finger, certify a printed sizer or determine whether a ring can be resized. Changing a chart input only changes the comparison; it does not establish a new physical measurement.