Country chart — United States & Canada

US ring size chart

The US and Canada system: plain numbers, in half-size steps, from 3 to 13.5. Canada uses the US chart with no conversion at all.

How the US system works

Numbers, not letters

US sizes are numbers from about 3 (small) to 13.5 (large) in the chart below. Larger numbers mean larger rings — there is no letter or circumference to decode.

Half sizes are the standard step

Each half size adds about 0.41 mm of inner diameter and about 1.3 mm of circumference. That is why a half size is the smallest step most US retailers stock.

Quarter sizes exist — retailer by retailer

Some retailers sell quarter sizes (for example 6.25 or 7.75). They are not in the published half-size ladder, so this site treats them as interpolated midpoints between half sizes in the converter, and never as published rows. If you have a quarter size, the millimetre diameter is the reliable version of it.

US chart — diameter and circumference

Scroll sideways to see all columns.

International ring size chart: US, UK, Australia, EU and India equivalents with inner diameter and circumference.
US / Canada	Inner diameter	Inner circumference
3	14.07 mm	44.2 mm
3.5	14.48 mm	45.5 mm
4	14.88 mm	46.7 mm
4.5	15.29 mm	48.0 mm
5	15.70 mm	49.3 mm
5.5	16.10 mm	50.6 mm
6	16.51 mm	51.9 mm
6.5	16.92 mm	53.2 mm
7	17.32 mm	54.4 mm
7.5	17.73 mm	55.7 mm
8	18.14 mm	57.0 mm
8.5	18.54 mm	58.2 mm
9	18.95 mm	59.5 mm
9.5	19.35 mm	60.8 mm
10	19.76 mm	62.1 mm
10.5	20.17 mm	63.4 mm
11	20.57 mm	64.6 mm
11.5	20.98 mm	65.9 mm
12	21.39 mm	67.2 mm
12.5	21.79 mm	68.5 mm
13	22.20 mm	69.7 mm
13.5	22.61 mm	71.0 mm

UK and EU equivalents for each row are on the international chart; this page isolates the US ladder so it can be read without cross-system noise.

Conversion examples

US 6 → 16.51 mm

Circumference 51.9 mm, UK L (approx.), EU 52. A common women's size.

US 7 → 17.32 mm

Circumference 54.4 mm, UK N (approx., N½ on half-letter charts), EU 54.

US 10 → 19.76 mm

Circumference 62.1 mm, UK T (approx.), EU 62. A common men's size.

Note: There is no simple formula for US sizes — the ladder is a published lookup table, not a straight line. That is why this site looks US sizes up instead of computing them from a formula, and why a US size converted to another system is always the nearest row, not an exact equivalent.

Original references

The US ladder in this chart matches the Primestyle published ladder to within 0.03 mm per row (rounding), and the Wikipedia ISO cross-check table to the same tolerance. No US standard document was freely available to cite directly; the ladder is therefore presented as a widely published retailer ladder, not as a quoted standard.

Related guides

International ring size chart
All systems on one table.
UK ring size chart
Letters, half letters, and why charts disagree.
Ring size converter
Convert a US size to any other system.