Converter · Centimetres
Ring size in cm
Most people who measure at home with a strip of paper and a school ruler end up with a figure in centimetres — 5.4 cm, say. That is a circumference, the distance around the finger, and it converts straight into a ring size. The table below does it, and the arithmetic underneath shows how.
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- US / CA
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- UK / AU
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- EU / ISO
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- India
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- Japan
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- Circumference
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No calibration needed — this is pure conversion. Measure now
The table
Finger circumference in cm to ring size
Find your measurement in the first column. If it falls between two rows, take the larger — a ring slightly loose can be adjusted, one that will not pass the knuckle cannot be worn.
| Circ. cm | Circ. mm | Ø mm | US / CA | UK / AU | EU / ISO |
|---|---|---|---|---|---|
| 4.42 | 44.2 | 14.1 | 3 | F | 44 |
| 4.55 | 45.5 | 14.5 | 3½ | G | 45 |
| 4.68 | 46.8 | 14.9 | 4 | H | 47 |
| 4.80 | 48.0 | 15.3 | 4½ | I | 48 |
| 4.93 | 49.3 | 15.7 | 5 | J | 49 |
| 5.06 | 50.6 | 16.1 | 5½ | K | 51 |
| 5.19 | 51.9 | 16.5 | 6 | L | 52 |
| 5.31 | 53.1 | 16.9 | 6½ | M | 53 |
| 5.44 | 54.4 | 17.3 | 7 | N | 54 |
| 5.57 | 55.7 | 17.7 | 7½ | O | 56 |
| 5.70 | 57.0 | 18.1 | 8 | P | 57 |
| 5.82 | 58.2 | 18.5 | 8½ | Q | 58 |
| 5.95 | 59.5 | 18.9 | 9 | R | 60 |
| 6.08 | 60.8 | 19.4 | 9½ | S | 61 |
| 6.21 | 62.1 | 19.8 | 10 | T | 62 |
| 6.33 | 63.3 | 20.2 | 10½ | U | 63 |
| 6.46 | 64.6 | 20.6 | 11 | V | 65 |
| 6.59 | 65.9 | 21.0 | 11½ | W | 66 |
| 6.72 | 67.2 | 21.4 | 12 | X | 67 |
| 6.85 | 68.5 | 21.8 | 12½ | Y | 68 |
| 6.97 | 69.7 | 22.2 | 13 | Z | 70 |
Derived from ISO 8653. One tenth of a centimetre — a single millimetre — is about 0.4 of a US size, so read the ruler carefully.
Doing it by hand
From centimetres to millimetres: multiply by 10. A 5.4 cm measurement is 54 mm, which is already your EU size, because the European scale is the circumference in whole millimetres.
From circumference to US size: subtract 36.537 and divide by 2.5535. So 54 mm gives (54 − 36.537) ÷ 2.5535 = 6.8, a US 6¾ to 7.
From circumference to diameter, if you would rather work across the ring: divide by π. 54 mm around is 17.2 mm across.
Why the paper strip disappoints
Three reasons a cm measurement reads small
- The strip pulls tight
- Paper compresses the flesh of the finger in a way a metal band never does. Wrap it snugly, not tightly, or you will be half a size under.
- The knuckle is not measured
- A strip round the base of the finger says nothing about whether the ring can get there. Check the knuckle separately and size for the larger of the two.
- A ruler reads to the millimetre at best
- That is about 0.4 of a US size of resolution, before parallax. Measuring an existing ring on a calibrated screen is roughly three times more precise.
In your market
The same circumference, in local numbers
Pick where you are ordering from. In Europe your centimetre reading is nearly the size already — 5.4 cm is an EU 54.
Do not know it? Measure a ring on your calibrated screen — it is the only number here that is not a conversion of another number.
Indian numeric
14
A number from 1 to about 30. Indian jewellers frequently print the UK letter beside it, because both are in daily use.
India. Indian jewellers quote a numeric scale of their own, roughly 1 to 30. Tanishq, Malabar Gold, Kalyan and GIVA all use it, and many print the UK letter beside it. Online-first brands often list US sizes as well, so check which scale a listing means before ordering. Full India ring size chart.
United States. The US numeric scale, sold mostly in half sizes. Quarter sizes exist and a jeweller can cut them, but they are rarely stocked. Full USA ring size chart.
United Kingdom. Letters, in half-letter steps. British hallmarked rings are usually stamped with the letter, so an inherited ring often tells you its own size if you look inside the band. Full UK ring size chart.
Europe. France, Germany, the Netherlands and Scandinavia quote the ISO 8653 number, which is the inside circumference in millimetres. Italy, Spain and Switzerland quote the same measurement minus 40, so a 54 becomes a 14. Full Europe ring size chart.
Japan. The Japanese numeric scale runs #1 to about #27 for the sizes people actually order. Mikimoto, Tasaki and 4°C all use it. Japanese sizes are usually whole numbers only. Full Japan ring size chart.
China. Mainland Chinese listings usually give 圈号 — the inside circumference in millimetres, the same number as EU/ISO. Hong Kong uses a separate numbered scale, and marketplace listings mix both with US sizes. Order by inside diameter in millimetres when a listing does not say which scale it means.
Australia. Australia and New Zealand use the UK letter scale unchanged, so a UK N is an Australian N.
Canada. Identical to the United States. A US 7 is a Canadian 7, with no conversion in between.
Singapore. Singapore retail is mixed: international brands quote US numbers, goldsmiths in the Chinese tradition quote Hong Kong numbers, and British-founded chains quote letters. Ask for the inside diameter in millimetres and you sidestep the whole problem.
Malaysia. As in Singapore, US numbers dominate modern retail while traditional goldsmiths use Hong Kong numbers. Confirm the scale, or the diameter, before you order.
United Arab Emirates. Gulf retail quotes US sizes most often. British-founded chains use letters, and the many Indian gold houses in Dubai use the Indian scale, so the same finger can be quoted three ways along one street.
South Africa. South Africa follows the UK letter scale. Online stores that ship from the United States will quote numbers instead.
Brazil. Brazilian sizes are the inside circumference in millimetres minus 40 — the same arithmetic Switzerland uses. A 54 mm circumference is a Brazilian 14.
Mexico. Mexican jewellers use a local numeric scale that is not the US one, and the published conversions for it disagree with each other. We will not print a number we cannot stand behind, so order by inside diameter in millimetres, or ask the retailer for the diameter of the size they are offering. Large chains and online stores generally quote US sizes.
Questions
Centimetres and ring sizes
What ring size is 5.4 cm?
54 mm of inside circumference — a US 6¾ to 7, a UK N to N½, and an EU 54.
What ring size is 6 cm?
60 mm of circumference, which is a US 9¼ and a UK S. In EU sizing it is simply a 60.
How do I measure ring size with a ruler?
Wrap a strip of paper about 6 mm wide round the base of the finger, mark where it overlaps, lay it flat and measure to the mark. That length is the circumference. Measuring a ring you already own is more accurate if you have one.
Is ring size in cm or mm?
The trade works in millimetres. Centimetres are what home measurements land in, so multiply by 10 and the rest of the chart applies.
Should I measure the finger or the knuckle?
Both, and size for the larger. The ring has to pass the knuckle to reach the base of the finger.
A ring you own beats a paper strip
It has one fixed inside diameter, it has already passed the knuckle test, and a calibrated screen reads it to about ±0.15 mm.