Round Cut Pave Setting Halo Lab Grown Diamond Engagement Ring (1.6 mm width)

Ring sizing systems differ by country, but they all describe the same physical thing: the inside circumference of the band in millimeters. Convert by finding your millimeter measurement, not by converting number to number — that is where mistakes creep in.

We size in US measurements. If you have a size from another system, use the chart below to find its US equivalent before ordering.

Conversion chart

How each system works

• US and Canada use a numeric scale in half-size steps. Each full size is roughly 0.4 mm of diameter, or about 1.3 mm of circumference.
• UK, Ireland, Australia and New Zealand use letters, with half sizes marked by a ½. The alphabet runs from A upward, so a UK L½ is a US 6.
• Europe (ISO 8653) is the most literal: the number is the inside circumference in millimeters, rounded. A European 52 is a band 52 mm around.
• Japan and China use their own numeric scale, which does not map evenly onto the others. Treat these as the closest match rather than an exact equivalent, and confirm against the millimeter columns.

Convert by millimeters, not by number

Systems round differently, and rounding twice compounds the error. If you know your size in one system, read across to the millimeter columns first, then find the nearest US size to that measurement. Where a measurement falls between two sizes, go up rather than down — a loose ring can be taken in, a ring that will not clear the knuckle cannot be worn.

Do not have a size in any system? Measure it at home in about five minutes.

Frequently asked questions

What is a UK size L in US sizing?

A UK L½ is a US 6, the most common women's size, with an inside diameter of 16.5 mm. A plain UK L sits just below that, between a US 5.5 and a US 6.

What does a European ring size number mean?

Under ISO 8653, the European size is the inside circumference of the band in millimeters. A European 52 is a ring measuring 52 mm around the inside, which corresponds to a US 6.

Are Japanese ring sizes the same as US sizes?

No. Japan uses a separate numeric scale that does not increase in step with the US one — a Japanese 11 is a US 6, but a Japanese 20 is a US 10. Always confirm against the millimeter measurement rather than assuming the numbers align.

How much bigger is a half size?

About 0.2 mm of inside diameter, or roughly 0.65 mm of circumference. It is a small difference on paper and a noticeable one on the finger.

Which sizes do you make?

Every ring is made in US half sizes from 3 to 13. Sizes outside that range are available on request — call (888) 709-7077.

Where to go next

• How to measure your ring size at home
• Printable US size chart
• How to resize a ring
• Shop engagement rings