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US ring size 12½

A US size 12½ ring is 21.79 mm (0.858") across the inside and 68.5 mm (2.70") round. It converts to UK Z, EU 68, Japan 27 and Swiss 28.5. The 1:1 circle below is already set to size 12½: lay a ring on it to check yours.

Try

Lay a ring that fits flat on the circle and size the red line until it just touches the inside edge of the band all the way round: on a phone, slide sideways anywhere on the stage or hold the buttons below; on a computer, drag the edge, scroll or press ← →. The gold ring is the band’s wall: don’t match its outside.

US 12½21.79 mm · 0.858" inside · 68.5 mm round
Inside diameter21.79 mm
Band wall1.8 mm
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Full chart 19 rows

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Size 12½ and the quarter sizes around it

9 rows
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US ring size 12.5 and quarter sizes within one size either side: inside diameter, difference in mm, circumference, UK and EU sizes
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20.98−0.81 mm65.9W½66
21.18−0.61 mm66.5X67
21.38−0.41 mm67.2X½67
21.59−0.20 mm67.8Y½68
21.79—68.5Z68
21.99+0.20 mm69.1Z½69
22.20+0.41 mm69.7Z+170
22.40+0.61 mm70.4Z+1½70
22.60+0.81 mm71.0Z+271

Ordering a size 12½ in different band widths

4 rows
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What size to order for a US size 12.5 finger in narrow, 4–6 mm, 7 mm and wider, and comfort-fit bands
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12½21.79Bands under 4 mm usually fit true to size.
12¾–1321.99–22.20A 4–6 mm band covers more skin and feels snugger: jewellers suggest a quarter to a half size up.
13–13½22.20–22.60Wide and cigar bands grip the whole finger segment: half a size to a full size up.
12–12¼21.38–21.59A domed comfort-fit inside slips over the knuckle more easily: often a quarter to a half size down.

Blank length for a size 12½ band

6 rows
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Length of wire or sheet to cut for a US size 12.5 ring band (21.79 mm inside) in stock 1.0 to 2.5 mm thick, by π × (inside diameter + thickness)
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71.62.819"23.79
72.22.844"24.19
73.22.881"24.79
74.12.918"25.39
74.72.942"25.79
76.33.004"26.79

05 / Field guide

Size 12½,
21.79 mm inside.

Everything about a US 12½: what it measures, who usually wears it, how it converts in each country, the quarter sizes around it and what to order for wide bands. Neighbouring sheets: size 12 and size 13.

Who wears a size 12½

A US 12½ is a large men’s size above the usual 9 to 12 range, also used for men’s thumb rings. Jewellers’ order data puts the most common women’s size at 7 and men’s at 10, so a 12½ is 5.5 sizes above the usual women’s size and 2.5 sizes above the usual men’s size. The same finger is often a quarter to half size larger on the dominant hand.

It is 0.41 mm wider inside than a 12 (21.38 mm) and 0.41 mm narrower than a 13 (22.20 mm). On the circumference that is 1.28 mm per half size, which is why a strip of string, stretching a couple of millimetres as you pull it snug, can misread a 12½ by most of a size.

Size 12½ in the UK, Europe and Japan

A 12½ is 68.5 mm round. UK letters on the BS 6820 scale cover 0.625 mm each with half sizes, and Z runs from 68.44 to 69.06 mm, so a 12½ sits near the bottom of Z. If you are on the small side of a 12½, a UK Y½ may suit better.

ISO 8653 rounds to the nearest millimetre, so EU 68 covers 67.5 to 68.5 mm and a 12½ lands 0.96 mm into that band. Swiss and Italian sizes subtract 40, giving 28.5. Japan 27 is 21.7 mm inside, 0.09 mm smaller than a US 12½, so Japanese 27 is the nearest match.

Quarter sizes either side

A 12¼ is 21.59 mm and a 12¾ is 21.99 mm, each about 0.2 mm from a 12½: roughly the thickness of two sheets of paper on the diameter. If your ring falls between 12¼ and 12¾ on the 1:1 circle, order a 12½ for a band under 4 mm.

For a 4–6 mm band, jewellers suggest 12¾ to 13; for 7 mm and wider, 13 to 13½; for a comfort-fit inside, 12 to 12¼. Smart-ring kits that include a size 13 sample: Oura Ring 4, Galaxy Ring, Ring AIR.

Making a size 12½ band

The blank length is the circumference of the middle of the band wall: π × (21.79 + thickness). Cut 73.2 mm of 1.5 mm stock or 74.7 mm of 2.0 mm stock, and the finished band has an outside diameter of 24.79 or 25.79 mm. Leave a little extra for filing the joint, and true the band on a mandrel at 12½ after soldering.

Blank = π × (21.79 mm + t) · 1.5 mm → 73.2 mm · 2.0 mm → 74.7 mm

Questions

Answered plainly.

01What is a size 12½ ring in mm?+

A US size 12½ ring is 21.79 mm (0.858") across the inside, with an inside circumference of 68.5 mm (2.70").

02What is a US size 12½ in UK and EU sizes?+

US 12½ is UK Z and EU (ISO 8653) 68. It is also Japan 27 and Swiss 28.5.

03How much bigger is a size 13 than a size 12½?+

A size 13 is 0.41 mm wider inside (22.20 against 21.79 mm) and 1.28 mm longer round.

04How long a blank do I cut for a size 12½ ring?+

73.2 mm for 1.5 mm thick stock and 74.7 mm for 2.0 mm, from π × (21.79 mm + thickness).

05Should I order a size 12½ for a wide band?+

For a band 7 mm or wider, jewellers suggest 13 to 13½; for 4–6 mm, 12¾ to 13. Under 4 mm, a 12½ fits true to size.

Ring sizesUS · inside Ø mm

Carat sizes

Necklace lengths