Ring Size Calculator and International Ring Size Chart
Use the ring size calculator to compare UK, Irish, Australian, New Zealand, US, Canadian, Swiss and selected Asian ring sizes using the inner diameter or inner circumference of a ring.
The chart also shows the whole-millimetre circumference size used in EU and ISO-style sizing. International equivalents are approximate because the different scales do not align exactly. For the most reliable fit, use a professional finger gauge or ask a jeweller to measure the ring or finger.
Table of Contents
- Ring Size Calculator
- International Ring Size Conversion Chart
- How to Measure Ring Size Accurately
- Ring Fit, Wide Bands and Finger Size
- Vintage and Antique Ring Sizing
- Ring Size FAQs
- Related Ring Guides and Jewellery
- About Ps Its Vintage
- References
Ring Size Calculator
Select the measurement or sizing system you already know. The calculator will return the closest row in the published conversion chart.
You can enter decimals or common fractions, including 8½, 8.5, P½, P 1/2, 17¾ or 17.75.
International Ring Size Conversion Chart
Compare inner diameter and circumference with UK, Irish, Australian, New Zealand, US, Canadian, EU or ISO, Swiss and selected Asian ring sizes. The calculator and chart use the same fixed conversion data.
Scroll sideways to view all columns. Scroll down inside the table while the gold column headings remain visible.
| Inner diameter in millimetres | Inner circumference in millimetres | UK, Ireland, Australia and New Zealand size | US and Canada size | EU or ISO circumference size | Switzerland size | Asian size shown in the GIA chart |
|---|---|---|---|---|---|---|
| 14.1 | 44.3 | F | 3 | 44 | 4 | 4 |
| 14.3 | 44.9 | F½ | 3¼ | 45 | 5¼ | 5 |
| 14.5 | 45.6 | G | 3½ | 46 | — | — |
| 14.7 | 46.2 | G½ | 3¾ | 46 | 6½ | 6 |
| 14.9 | 46.8 | H | 4 | 47 | — | 7 |
| 15.1 | 47.4 | H½ | 4¼ | 47 | 7¾ | — |
| 15.3 | 48.1 | I | 4½ | 48 | — | 8 |
| 15.5 | 48.7 | I½ | 4¾ | 49 | 9 | — |
| 15.7 | 49.3 | J | 5 | 49 | — | 9 |
| 15.9 | 50.0 | J½ | 5¼ | 50 | 10 | — |
| 16.1 | 50.6 | K | 5½ | 51 | — | 10 |
| 16.3 | 51.2 | K½ | 5¾ | 51 | 11¾ | — |
| 16.5 | 51.8 | L | 6 | 52 | 12¾ | 11 |
| 16.7 | 52.5 | L½ | 6¼ | 53 | — | 12 |
| 16.9 | 53.1 | M | 6½ | 53 | 14 | 13 |
| 17.1 | 53.7 | M½ | 6¾ | 54 | — | — |
| 17.3 | 54.3 | N | 7 | 54 | 15¼ | 14 |
| 17.5 | 55.0 | N½ | 7¼ | 55 | — | — |
| 17.7 | 55.6 | O | 7½ | 56 | 16½ | 15 |
| 17.9 | 56.2 | O½ | 7¾ | 56 | — | — |
| 18.1 | 56.9 | P | 8 | 57 | 17¾ | 16 |
| 18.3 | 57.5 | P½ | 8¼ | 58 | — | — |
| 18.5 | 58.1 | Q | 8½ | 58 | — | 17 |
| 18.8 | 59.1 | Q½ | 8¾ | 59 | — | 19 |
| 19.0 | 59.7 | R | 9 | 60 | — | 18 |
| 19.2 | 60.3 | R½ | 9¼ | 60 | 20¼ | — |
| 19.4 | 60.9 | S | 9½ | 61 | — | 19 |
| 19.6 | 61.6 | S½ | 9¾ | 62 | 21½ | — |
| 19.8 | 62.2 | T | 10 | 62 | — | 20 |
| 20.0 | 62.8 | T½ | 10¼ | 63 | — | 21 |
| 20.2 | 63.5 | U | 10½ | 64 | 22¾ | 22 |
| 20.4 | 64.1 | U½ | 10¾ | 64 | — | — |
| 20.6 | 64.7 | V | 11 | 65 | — | 23 |
| 20.8 | 65.3 | V½ | 11¼ | 65 | — | 25 |
| 21.0 | 66.0 | W | 11½ | 66 | — | 24 |
| 21.2 | 66.6 | W½ | 11¾ | 67 | — | — |
| 21.4 | 67.2 | X | 12 | 67 | 27½ | 25 |
| 21.6 | 67.9 | X½ | 12¼ | 68 | — | — |
| 21.8 | 68.5 | Y | 12½ | 69 | 28¾ | 26 |
| 22.0 | 69.1 | Z | 12¾ | 69 | — | — |
| 22.2 | 69.7 | Z½ | 13 | 70 | — | 27 |
| 22.4 | 70.4 | — | 13¼ | 70 | — | — |
| 22.6 | 71.0 | Z+1 | 13½ | 71 | — | — |
These are conversion equivalents rather than a guarantee of fit. Band width, internal profile, finger shape, temperature and previous resizing can all affect how a ring feels.
How to Measure Ring Size Accurately
The most reliable option is to have the finger measured by a jeweller using a professional finger gauge. To identify the size of an existing ring, a jeweller can use a calibrated ring stick or mandrel.
Measuring an existing ring at home
- Choose a ring that fits the intended finger comfortably.
- Check that the ring is perfectly round. An oval or distorted ring will not give a dependable single diameter measurement.
- Use digital callipers if possible and measure the empty internal space across the centre of the ring.
- Do not include the metal edges in the measurement.
- Measure more than once and enter the result in millimetres to one decimal place.
For a more detailed explanation, read How to Measure Your Ring Size Accurately (Even When It Changes).
Ring Fit, Wide Bands and Finger Size
A ring should be loose enough to pass over the knuckle and then sit securely where it will be worn. Finger size can change with temperature, humidity, activity and time of day, so avoid measuring when your hands are unusually cold, hot or swollen.
Rings wider than 4 mm require different fitting consideration from narrow rings. A wide-band finger gauge is more reliable than automatically adding a fixed half size.
The internal profile also matters. A curved interior, flat interior, open shank or setting that projects into the finger opening can affect how the measured size feels.
Vintage and Antique Ring Sizing
Vintage and antique rings may have been resized previously, and an older shank may be slightly oval or uneven. This can make a single inner diameter measurement less reliable than it would be on a perfectly round modern ring.
Many rings can be resized by a skilled jeweller, but the safe adjustment depends on the metal, design, stone setting and condition. Full eternity rings, patterned or engraved shanks, enamelled rings and pieces with delicate settings can be more limited.
Any valuable or unusual ring should be assessed before alteration. Resizing may affect hallmarks, engraving, symmetry or the security of stones if the work is not suitable for the design.
Browse antique, vintage and preloved rings to see the size and available details for each individual piece.
Ring Size FAQs
Select the measurement or sizing system you already know, enter the value and choose Convert Ring Size. The calculator returns the closest row in the chart and highlights it.
Yes. Australia uses the same letter-based scale as the UK. Ireland and New Zealand also commonly use this letter system, so the same chart column applies.
UK size P is approximately US size 8. It corresponds to an inner diameter of about 18.1 mm, an inner circumference of about 56.9 mm and EU or ISO circumference size 57.
An 18.0 mm inner diameter falls between UK O½ at 17.9 mm and UK P at 18.1 mm. The nearest row in this chart is UK P, but an in-person measurement is preferable when fit is important.
EU or ISO circumference size 57 is closest to UK size P and US size 8 in this chart, with an inner diameter of approximately 18.1 mm.
The UK, Ireland, Australia and New Zealand commonly use letters. The US and Canada use numbers. EU or ISO-style sizing uses the ring's inner circumference in millimetres.
The Asian column follows the GIA chart grouping for Hong Kong, China, Singapore, Taiwan and Japan. Local jewellers may use different conventions, so treat it as a conversion guide rather than a guarantee of fit.
The GIA international chart does not provide a direct Swiss or Asian equivalent for every UK or US row. A dash is shown rather than inventing a value.
Inner diameter is usually the easiest home measurement when you have a perfectly round ring that already fits. Inner circumference is the measurement used for EU or ISO-style sizing.
A professional finger gauge is the most reliable way to measure a finger. A calibrated ring stick or mandrel is used to measure an existing ring.
It returns the closest published chart equivalent. It cannot guarantee physical fit because national scales do not align exactly and band width, internal profile, finger shape and temperature can affect the result.
Do not automatically choose the larger size. Consider the knuckle, band width, internal profile and preferred fit, and ask a jeweller to check the finger when the ring is valuable or difficult to resize.
Measure more than once when your hands are at a comfortable, normal temperature. Avoid measuring when your fingers are unusually cold, hot or swollen.
A wide band can feel tighter than a narrow ring of the same measured size. Use a wide-band finger gauge or ask a jeweller to assess the fit instead of automatically adding a fixed amount.
Yes. Ring size systems apply to everyone. The correct fit depends on the finger, knuckle, band width, internal profile and preferred fit.
National sizing systems use different intervals and do not align exactly. Charts may also round diameter or circumference differently, so an international equivalent should be treated as the closest conversion rather than a guaranteed identical size.
They provide only a rough estimate. String can stretch, paper can bend or change with moisture, and neither method properly accounts for the knuckle.
Many can be resized, but the safe adjustment depends on the metal, shank, setting and condition. Full eternity rings, enamel, continuous patterns, engraving and delicate stone settings can limit the work.
About Ps Its Vintage
Ps Its Vintage is independently run and specialises in preloved, vintage and antique jewellery. I sell lockets, rings, chains, brooches, bracelets, earrings, charms and small collectable pieces, with new pieces added as I find them.
Each ring is described with the available information about its materials, hallmarks, measurements, age, condition and ring size, so you can understand the piece before buying. This guide is intended to help compare international ring sizes and explain the factors that can affect how a ring fits.
More about the business can be found on the About Ps Its Vintage page.