Should I size up for wide bands?

Yes. Bands wider than ~6mm fit more snugly than thin bands at the same nominal size; jewelers typically suggest going up half a size when the band is over 6mm or comfort-fit.

Are knuckle-larger fingers a problem?

Often. Size the ring to slide over the knuckle, but be aware it may spin loosely at the base. Jewelers can add tiny weights or a ring-sizing bar to compensate.

How accurate is the paper-strip method?

Reasonable — typically within half a size — provided you measure cold-finger and after sliding the strip up over your knuckle. Cold and post-exercise fingers can differ by a full size.

Does the converter handle plus sizes (US 14+)?

Not yet — the curated table runs 3 to 13. Tell us via the contact page if you want extended sizing.

Does the calculator store my measurement?

No. Everything stays in your browser.

Ring Size Converter

US ↔ UK ↔ EU ↔ JP, with inner diameter as the universal anchor.

Every regional ring size is just a label on the band’s inner diameter. The widget below works in either direction: enter a US size and see the equivalents, or measure the inside diameter of a ring that fits and look up the right size in any system. Half-sizes are supported on the US scale, which is more granular than UK or EU.

US size (3–13, half steps)

EU / JP

Diameter

17.3 mm

Circumference: 54.3 mm

Measure your finger at the end of the day, when it’s largest. Avoid measuring when cold — fingers shrink by up to half a size in winter.

How to use

Measure a ring that fits
Lay it flat and measure across the inside in millimeters. That's the diameter — the universal measurement.
Or, measure your finger
Wrap a strip of paper around the base of your finger, mark where it overlaps, then measure the length. That's the circumference; the widget converts.
Read the cross-region size
All four regions display side-by-side. US uses half-sizes; UK uses single letters with halves; EU and JP use the circumference in mm.

Quick reference

US	UK	EU / JP	Diameter
5	J 1/2	49	15.7 mm
6	L 1/2	52	16.5 mm
7	N	54	17.3 mm
8	P	57	18.2 mm
9	R	60	19.0 mm
10	T	62	19.8 mm
11	V	65	20.6 mm

Frequently asked questions

Should I size up for wide bands?: Yes. Bands wider than ~6mm fit more snugly than thin bands at the same nominal size; jewelers typically suggest going up half a size when the band is over 6mm or comfort-fit.
Are knuckle-larger fingers a problem?: Often. Size the ring to slide over the knuckle, but be aware it may spin loosely at the base. Jewelers can add tiny weights or a ring-sizing bar to compensate.
How accurate is the paper-strip method?: Reasonable — typically within half a size — provided you measure cold-finger and after sliding the strip up over your knuckle. Cold and post-exercise fingers can differ by a full size.
Does the converter handle plus sizes (US 14+)?: Not yet — the curated table runs 3 to 13. Tell us via the contact page if you want extended sizing.
Does the calculator store my measurement?: No. Everything stays in your browser.

About

Why diameter is the anchor

All four regional systems are conventions layered on top of a physical measurement. Diameter (the inside straight-line width of the band) is the simplest one to measure, and circumference = π × diameter follows from it. Regional sizes are just rounded labels on those mm values.

Tolerance

Even within one system, a half-size step is roughly 0.4 mm in diameter — about the thickness of a credit card edge. Tiny differences move you between sizes; a degree of fit-tolerance comes with the territory of mass-produced jewelry.