Ring Size Chart: US, UK, EU and Japan Sizes with Diameter and Circumference

Ring size chart: US, UK, EU and Japan

All four systems measure the same thing, the inside of the ring. The US scale steps by diameter, Europe uses the circumference in millimeters, the UK uses letters roughly 1.25 mm of circumference apart, and Japan uses numbers about 1 mm apart. Find your inside diameter or circumference in the middle columns, then read across.

The US formula is inside diameter = 0.458 in + 0.032 in × size, so size 0 is 11.6 mm and every whole size adds 0.81 mm. Quarter sizes exist in the US and Canada and add 0.2 mm each. UK sizes above Z continue as Z+1, Z+2 and so on, used mainly for men's rings.

How to measure your ring size at home

A string or paper strip around the finger is the most common home method and the least reliable, because paper does not compress the way a metal band does and it is easy to pull too tight. Measuring a ring that already fits is far more accurate.

1. Use a ring that fits the same finger. Lay it on a millimeter ruler and read the inside edge to inside edge across the widest point. Do not include the metal. Find that number in the diameter column above.
2. If you have no ring, wrap a strip of paper about 5 mm wide around the base of the finger, snug enough that it would just slide over the knuckle. Mark the overlap with a pen and measure the length in mm. That is your circumference; match it in the circumference column.
3. Check the knuckle. If your knuckle is much wider than the base of the finger, take a second measurement over the knuckle and choose a size between the two. The ring has to pass the knuckle but should not spin freely at the base.
4. Measure at the right time. Fingers are larger in the evening, in heat and after exercise or salty meals, and smaller in cold weather. Measure at room temperature in the afternoon or evening, and repeat on a second day.
5. Round up between sizes for wide bands. A band 6 mm or wider covers more of the finger and feels about half a size tighter than a 2 mm band of the same size.

A printed ring sizer works only if the printer prints at 100% scale. Check it by measuring a printed reference line with a ruler before you use it. Plastic adjustable sizers, sold cheaply, are more reliable than paper because they behave like a band.

How big each ring size is in real life

A diameter of 17 mm sounds abstract. Comparing against an object of known size gives a quick sanity check before you order.

If a dime slides through a ring with a little room, the ring is a size 8 or larger. If the dime will not pass at all, the ring is size 7½ or smaller.

Ring sizes for men, women and children

Ring sizes are unisex. The same US size 9 means the same 18.9 mm inside diameter on a man's band or a woman's ring. What differs is the range each group falls into and the band widths they tend to wear.

Thumb rings run well above the wearer's ring-finger size, often by 2 to 4 sizes, and thumbs vary more than any other finger. Measure the thumb directly, over the knuckle as well as at the base.

Ring size by finger and hand

If you know your size on one finger, you can estimate the others, then confirm with a measurement. The offsets below are typical, not fixed.

• Ring finger: the reference size for engagement rings and wedding bands.
• Middle finger: usually 1 to 1½ sizes larger than the ring finger.
• Index finger: usually ½ to 1 size larger than the ring finger.
• Little finger: usually 1½ to 2½ sizes smaller than the ring finger.
• Thumb: usually 2 to 4 sizes larger than the ring finger, with a large knuckle to clear.
• Dominant hand: often about ½ size larger than the same finger on the other hand.

Midi rings, worn above the middle knuckle, are typically 3 to 4 sizes smaller than the finger's base size.

How band width changes the size you need

The size number describes only the inside diameter, but a wide band touches more of the finger, has to slide over the knuckle as a stiffer tube, and traps more moisture. Jewelers commonly adjust for that.

Comfort-fit bands, which are rounded on the inside, slide over the knuckle more easily and often feel looser than a flat-inside band of the same size. Wedding band widths, profiles and fit are covered in detail in the wedding band size guide.

Resizing: how far a ring can go

A jeweler resizes a metal band by cutting it and adding or removing a piece of metal, or by stretching or compressing it slightly on a mandrel. How far that can go depends on the ring.

If a ring cannot be resized, internal sizing beads or a spring insert can take up a half size or so of looseness. For rings bought as a surprise, the engagement ring size guide covers ways to find a size without asking.

Common ring sizing mistakes

• Measuring the outside of a ring. A 2 mm thick band adds 4 mm to the outer diameter, which is five US sizes.
• Reading diameter as circumference. If a number between 40 and 75 comes out, it is a circumference in mm (or an EU size). A diameter will be between about 12 and 24 mm.
• Using string. String stretches and digs in. A paper strip or a plastic sizer gives a truer reading.
• Measuring cold fingers. A ring sized in winter can be tight in summer, and the reverse can mean a lost ring.
• Mixing up UK and US sizes. UK sizes use letters, so a request for a size P is a US 8, not a typo.

Rings are only one part of fitting jewelry. Wrist measurements for bracelets and chain lengths for necklaces follow different rules, and a ring dish or compartments in a jewelry box help keep sized rings from scratching each other.

Frequently asked questions