Different countries. The same perfect fit.
US, UK, EU and JP sizes, with inner diameter in mm and inches.
Choose your sizing system and size.
16.5 mm / 0.650 in inner diameter
Half sizes included. Inner diameter is your best reference.
| US | UK | EU ≈ | JP | Inner Ø mm | Inner Ø in |
|---|---|---|---|---|---|
| 3 | F | 44 | 4 | 14.1 | 0.555 |
| 3.5 | G | 46 | — | 14.5 | 0.571 |
| 4 | H | 47 | 7 | 14.9 | 0.587 |
| 4.5 | I | 48 | 8 | 15.3 | 0.602 |
| 5 | J | 49 | 9 | 15.7 | 0.618 |
| 5.5 | K | 51 | 10 | 16.1 | 0.634 |
| 6 | L | 52 | 11 | 16.5 | 0.650 |
| 6.5 | M | 53 | 13 | 16.9 | 0.665 |
| 7 | N | 54 | 14 | 17.3 | 0.681 |
| 7.5 | O | 56 | 15 | 17.7 | 0.697 |
| 8 | P | 57 | 16 | 18.1 | 0.713 |
| 8.5 | Q | 58 | 17 | 18.5 | 0.728 |
| 9 | R | 60 | 18 | 19.0 | 0.748 |
| 9.5 | S | 61 | 19 | 19.4 | 0.764 |
| 10 | T | 62 | 20 | 19.8 | 0.780 |
| 10.5 | U | 63 | 22 | 20.2 | 0.795 |
| 11 | V | 65 | 23 | 20.6 | 0.811 |
| 11.5 | W | 66 | 24 | 21.0 | 0.827 |
| 12 | X | 67 | 25 | 21.4 | 0.843 |
| 12.5 | Y | 68 | 26 | 21.8 | 0.858 |
| 13 | Z½ | 70 | 27 | 22.2 | 0.874 |
| 13.5 | Z+1 | 71 | — | 22.6 | 0.890 |
| 14 | — | 72 | — | 23.0 | 0.906 |
| 14.5 | — | 74 | — | 23.4 | 0.921 |
| 15 | — | 75 | — | 23.8 | 0.937 |
Reference: GIA international chart; US 14–15 diameters: Peter Stone. EU values are inner circumference (π × diameter), rounded to the nearest mm. “—” means no mapping is available in our reference. Brand charts may differ.
Your ring tells you the rest. Find its size on screen.
Find the system you already know, then read across the row. If you have an inside measurement, start with the diameter column.
Measure the inside, not the outside. The metal band adds width to the outer diameter without changing the fit.
Repeat the measurement and consider the band. Wider bands tend to feel tighter. Fingers also change with temperature and time of day.
Check the retailer’s fit guidance, especially for an expensive ring or a design that cannot be resized.
They use different scales, so conversions are a guide.
A numeric scale, often sold in half sizes. Our chart covers US 3 to 15.
A letter scale. Different published conversion charts may place a US size at a different letter.
EU 52 refers to about 52 mm around the inside of a ring, not 52 mm across it.
Japanese sizes are not US sizes. Blank entries mean the source does not list an equivalent.
Straight answers about diameter, circumference and international sizes.
Check the conversion chartNumeric answers use the same reference data as the chart above.
GIA ring sizing referenceFind the size you know in the corresponding column and read across the same row, or use the selector above. These are approximate conversions from the cited reference tables. Check the retailer’s own chart before ordering.
Our reference lists US 7 with an inner diameter of 17.3 mm, or 0.681 inches. Its calculated inner circumference is about 54.3 mm. Diameter is the distance across the opening; circumference is the distance around it.
In the GIA reference table used here, US 7 maps to UK N. Our rounded circumference reference is EU approximately 54. Letter conversions can differ between retailer charts, so confirm with the seller.
A 17.0 mm inner diameter is closest to US 6.5 in our half-size table, whose reference diameter is 16.9 mm. Its measured circumference is about 53.4 mm. Keep the original 17.0 mm measurement when checking the seller’s chart; the nearest size is an approximation.
A 54 mm circumference is an equivalent diameter of about 17.19 mm, using diameter = circumference ÷ π. The closest half size in our table is US 7. This is a conversion of your measurement, not a guarantee of fit; verify a paper-strip estimate with a finger gauge or jeweler.
Both describe the inside opening, but they are different measurements. Inner diameter runs straight across the opening; inner circumference runs around it. Circumference = diameter × π. Do not compare a finger circumference with the diameter column.
Multiply an inner diameter in inches by 25.4 to get millimetres, then find the closest diameter in the chart. If you measured around your finger instead, that is circumference: convert it to millimetres and divide by π before using the diameter column.
In the GIA reference table used here, US 6 corresponds to UK L and an inner diameter of 16.5 mm. Other retailers may use different letter conversions. Use the seller’s chart for the ring you plan to buy.
The measurement and sizing scale are the same within a given system. A US size number does not change because a ring is sold for men or women. Measure the intended finger and consider the band width rather than choosing by an average.
Look for clearly labelled inner measurements, an identified data source and the correct sizing system. This chart cites GIA and Peter Stone. Conversions and brand fits can differ, so the retailer’s chart and a physical fitting are the final checks.
Use finger mode on the homepage for a visible-width estimate without an existing ring. This is not a circumference measurement or guaranteed fit. For a physical finger measurement, use a finger gauge or ask a jeweler to check the intended finger and knuckle.