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Ring Size Chart

Match your ring size across US, UK, EU and Japan systems in one click.

Privacy: your files never leave your device. All processing happens locally in your browser.

How to use

  1. 1.Choose the sizing system you already know — US/Canada, UK/Australia, EU/ISO or Japan — from the first dropdown, then select your size.
  2. 2.Or measure a ring you already own: lay it flat and measure straight across the inside from edge to edge in millimeters — that distance is the inner diameter. Switch the input to Inner diameter and enter the value (inches are also accepted).
  3. 3.Read the results table for the matching size in every system, including inner diameter and inner circumference. For measured values, the tool also flags the nearest standard ring size.

About Ring Size Chart

The ring size converter turns a single ring measurement into its equivalents across every major sizing system, so you can shop or order a ring anywhere in the world without guessing. Ring sizing is fragmented: the United States and Canada use a numeric scale (typically 3 to 13.5 in half steps), the United Kingdom and Australia use letters (A through Z and beyond), most of Europe follows the ISO 8653 standard where the size number equals the inner circumference in millimeters, and Japan uses its own numeric scale. On top of those national systems, the two measurements that actually matter physically are the ring's inner diameter and its inner circumference, both in millimeters. This tool holds all of those in a single cross-checked reference table and lets you enter any one of them to see the rest instantly.

Pick the system you already know from the dropdown — US/Canada, UK/Australia, EU/ISO, or Japan — choose your size, and the converter shows the matching size in every other system alongside the exact inner diameter and inner circumference. If instead you have measured a ring rather than looked up a printed size, switch the input to inner diameter or inner circumference, type the millimeter value (diameter also accepts inches), and the tool finds the nearest standard size for you. Because a measured value rarely lands exactly on a catalog size, the result panel tells you which standard size is closest so you can round with confidence.

The math behind the table is simple and transparent. The inner circumference is always the inner diameter multiplied by pi, so a 17.3 mm diameter corresponds to roughly 54.4 mm of circumference. Under ISO 8653, the European size number is essentially that circumference in millimeters, which is why a US 7 lands near EU 54. The Japanese scale tracks the diameter closely as well. Every row in this converter is derived from the same underlying diameter and cross-checked against reputable jeweler charts, so the numbers stay internally consistent rather than being copied by hand from mismatched sources.

Everything runs entirely in your browser. There is no upload, no account, and no data leaves your device — the whole reference table and conversion logic ship with the page and compute locally the moment you change an input. That makes the tool fast, private, and usable offline once the page has loaded.

A word of caution that matters for anyone buying a ring: this is a guide, not a guarantee. Real ring sizes vary slightly between jewelers, countries, and even between styles from the same maker, because band width, profile, and manufacturing tolerances all shift the effective fit. Wide or comfort-fit bands generally need a size larger than a thin band. Fingers also change size with temperature, time of day, and season. For an engagement ring or any costly purchase, use this converter to get close, then confirm the final size with a jeweler using a physical ring sizer or mandrel before you order. Treat the equivalents here as a reliable starting point for comparison shopping across international sizing systems.

Frequently asked questions

How do I measure my ring size at home?
Two easy ways. To use a ring that already fits, lay it flat and measure the inside straight across, edge to edge, in millimeters — that is the inner diameter. To measure a finger directly, wrap a thin strip of paper or string around it, mark where it overlaps, and measure the length in millimeters — that is the inner circumference. Enter either value here to find your size. Measure at the end of the day when fingers are largest, and repeat two or three times for accuracy.
How accurate is this ring size converter?
It is a general guide based on ISO 8653 sizing and standard jeweler charts, and it is internally consistent (circumference equals diameter times pi). However, real sizes vary slightly between jewelers, countries and ring styles. Wide or comfort-fit bands usually need a size larger than a thin band, and fingers change with temperature and time of day. For an engagement ring or any expensive purchase, confirm the final size with a jeweler using a physical ring sizer before ordering.
What is a US size 7 ring in UK, EU and Japan sizes?
A US/Canada size 7 is approximately UK/Australia N½, EU/ISO 54, and Japan 14. Physically that is about a 17.3 mm inner diameter and a 54.4 mm inner circumference. These are close equivalents; letter sizes in particular can shift by half a size between different jeweler charts.

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