What Is a Ring Size Table Converter?
A ring size table converter translates a ring size from one regional sizing system into the nearest equivalent used in another country. The same physical ring can be described by a UK letter, a US/Canada number, a European circumference-based value or a Japanese number depending on where it is sold.
The most reliable way to compare those systems is to use the ring's inside diameter or inside circumference as the common reference. Once the physical opening is known, each regional label can be matched to that measurement.
International conversion is approximate because different systems use different increments. One UK half size can fall between two available values elsewhere, while an EU value may round circumference to a whole millimetre. Use the tool below for a close measurement-based match, then check the seller's own size chart before ordering.
Convert UK, US, EU and Japan Ring Sizes
Choose the sizing system you already know and select your current size.
Conversion note: Different sizing systems do not share identical increments. Treat the result as the nearest measurement match and verify the retailer's own sizing chart for a final purchase.
Inside Diameter → Circumference
Inside Circumference → Diameter
| Inside Diameter | Inside Circumference | UK / Ireland | US / Canada | EU / ISO-Style | Japan |
|---|
Note: The chart uses physical measurement as the common reference. UK values are matched to the nearest US, EU and Japan values, so another retailer may show a slightly different rounded equivalent.
UK / Ireland
Uses letters such as K, L, M and N, with many charts including half sizes such as L½ or N½.
US / Canada
Uses a numerical scale with full, half and sometimes quarter-size increments.
EU / ISO-Style
Many continental European references use values closely tied to internal circumference in millimetres.
Japan
Uses a separate numerical system. Similar-looking numbers should not be confused with North American sizes.
The purpose of a ring size table converter is to translate between these different labels without pretending that the labels themselves are universal. A UK N and a US 7 do not share the same symbol, but their physical openings can be close enough to serve as practical equivalents.
European standardization also matters. EN ISO 8653:2026 provides a common European reference for ring-size definition, measurement and designation, helping reduce ambiguity in cross-border jewellery sales. Even with standardization, shoppers can still encounter older national systems and retailer-specific conversion tables.
The physical opening stays the same — the regional label changes
International conversion works best when every label is tied back to a common inside measurement.
Start With a Known Size
Choose the UK, US, EU or Japan value you already know.
Translate to Measurement
The tool identifies the approximate inside circumference behind the size.
Match Other Systems
The same measurement is compared with the nearest size in each target system.
If you know only the physical ring and not its labelled size, measure the ring before converting. An existing ring that fits the intended finger can provide a useful inside-diameter reference. A jeweller can provide a more precise measurement using a ring mandrel or finger-gauge set.
Use the correct finger
Choose a ring that fits the exact hand and finger where the new ring will be worn.
Measure the inside opening
Measure straight across the internal edges. Do not include the metal band.
Use millimetres
Ring size differences are small, making millimetres more useful than rough inch measurements.
Calculate circumference
Multiply inside diameter by π, or use the converter above.
Find the nearest row
Compare that measurement with the complete international ring size table.
Verify with the seller
Check the retailer's own chart before buying, especially for custom or difficult-to-resize rings.
Useful ring-size formulas
The converter needs the empty internal opening
Outside diameter includes ring metal and will make the size appear too large.
Inside Edge to Inside Edge
Measure only the empty opening where the finger sits.
Exclude Metal Thickness
Outside diameter includes both sides of the ring band and produces the wrong result.
Use a Fine Scale
A precise millimetre ruler or caliper helps distinguish small ring-size differences.
UK to US ring size conversion
If you wear UK N, the converter first maps that letter to an approximate circumference and then finds the nearest North American number. Because the systems use different steps, the nearest result may sit around US 6¾ to 7 depending on the chart and rounding method.
US to EU ring size conversion
A US size near 7 corresponds to an internal circumference in the mid-54 mm range. That puts it close to an EU/ISO-style value around 54 or 55, depending on how the retailer rounds.
Diameter to international ring size
If an existing ring measures about 17.2 mm across the inside, its circumference is about 54.0 mm. That measurement can then be compared across UK, US, EU and Japan labels without needing to know the original regional size.
Japan to UK or US conversion
Japanese sizes use a numerical scale that is different from the North American scale. Always convert through a physical measurement rather than assuming that similar-looking numbers represent similar ring openings.
Two reputable ring conversion charts can show slightly different equivalents because the underlying systems do not divide ring circumference into identical increments. A measurement that sits neatly on one UK half size can fall between available values in Japan or North America.
Different increments and rounding
UK sizing commonly uses letters and half sizes. North American charts may include full, half or quarter sizes. EU/ISO-style values are closely associated with circumference in millimetres. Converting between these scales often means choosing the nearest commercial label rather than an exact mathematical twin.
Manufacturing and retailer tolerance
Real rings are manufactured objects, and brands may publish slightly different nominal measurements or round them differently. This is why the retailer's own chart should be the final reference for an online order.
Finger size also changes
Temperature, time of day and the exact hand can affect fit. GIA advises using proper finger gauges and notes that professional sizing removes much of the uncertainty that comes from home measurements.
- Identify the seller's sizing system. A bare number such as 7 is meaningless until you know whether it is US, Japan or another scale.
- Convert your known size to circumference or diameter. Physical measurement gives you a universal reference point.
- Read the seller's own chart. Use this converter as a bridge, then verify how the retailer labels the measurement.
- Check the available increments. Some shops sell only whole sizes, while others offer half or quarter sizes.
- Consider band width. Wide rings may feel tighter than narrow rings with the same nominal measurement.
- Review resize and exchange policies. This matters for international shipping, custom rings and difficult-to-resize materials or settings.
If you do not know your size yet, start with our UK Ring Size Calculator, then use this international table to convert the result. For broad or chunky designs, also read the Ring Size Guide for Wide Bands.
The mathematical conversion describes the nominal ring opening, but it does not guarantee that every ring with that opening will feel identical. A wider shank covers more of the finger and can feel tighter than a slim ring of the same nominal size.
GIA notes that wide shanks generally fit more snugly and that bridal sets wider than about 4–5 mm require special consideration. If you are buying a 6 mm, 8 mm or 10 mm ring, first convert the nominal size and then test a same-width or wide-finger sizing gauge before ordering.
Trust Measurements
Use inside diameter or circumference as the common reference when regional labels disagree.
Check the Retailer
Compare the converted result with the seller's own chart before placing an order.
Use the Correct Finger
Corresponding fingers on opposite hands can differ, so measure the intended hand.
Avoid Extreme Temperature
Cold fingers shrink and warm fingers can swell, affecting the measured fit.
Measure the Inside
When using an existing ring, exclude the metal and measure the empty opening.
Confirm Valuable Rings
Professional sizing is worthwhile for expensive, custom or difficult-to-resize jewellery.
Watch Wide Bands
A correct nominal conversion can still feel tighter when the band covers more finger area.
Check Returns
International purchases are easier when the retailer has a clear size-exchange policy.
This page uses a measurement-first approach and nearest-size matching. The following external references explain professional sizing methods, international conversion and current European standardization:
- GIA 4Cs — How to Determine Ring Size
- GIA — Accurate Determination of Finger and Ring Sizes
- Blue Nile — Ring Size Chart & Conversion Guide
- CEN-CENELEC — EN ISO 8653:2026
- ISO — ISO 8653:2016