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US ring size 8½

A US size 8½ ring is 18.54 mm (0.730") across the inside and 58.2 mm (2.29") round. It converts to UK Q½, EU 58, Japan 18 and Swiss 18. The 1:1 circle below is already set to size 8½: 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 8½18.54 mm · 0.730" inside · 58.2 mm round
Inside diameter18.54 mm
Band wall1.8 mm
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Full chart 19 rows

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Size 8½ and the quarter sizes around it

9 rows
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US ring size 8.5 and quarter sizes within one size either side: inside diameter, difference in mm, circumference, UK and EU sizes
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17.73−0.81 mm55.7O½56
17.93−0.61 mm56.3P56
18.13−0.41 mm57.0P½57
18.34−0.20 mm57.6Q58
18.54—58.2Q½58
18.74+0.20 mm58.9R59
18.95+0.41 mm59.5R½60
19.15+0.61 mm60.2S60
19.35+0.81 mm60.8S½61

Ordering a size 8½ in different band widths

4 rows
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What size to order for a US size 8.5 finger in narrow, 4–6 mm, 7 mm and wider, and comfort-fit bands
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8½18.54Bands under 4 mm usually fit true to size.
8¾–918.74–18.95A 4–6 mm band covers more skin and feels snugger: jewellers suggest a quarter to a half size up.
9–9½18.95–19.35Wide and cigar bands grip the whole finger segment: half a size to a full size up.
8–8¼18.13–18.34A domed comfort-fit inside slips over the knuckle more easily: often a quarter to a half size down.

Blank length for a size 8½ band

6 rows
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Length of wire or sheet to cut for a US size 8.5 ring band (18.54 mm inside) in stock 1.0 to 2.5 mm thick, by π × (inside diameter + thickness)
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61.42.417"20.54
62.02.441"20.94
63.02.478"21.54
63.92.516"22.14
64.52.540"22.54
66.12.602"23.54

05 / Field guide

Size 8½,
18.54 mm inside.

Everything about a US 8½: 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 8 and size 9.

Who wears a size 8½

A US 8½ is the upper half of the women’s range and below most men’s sizes (9 to 12). Jewellers’ order data puts the most common women’s size at 7 and men’s at 10, so a 8½ is 1.5 sizes above the usual women’s size and 1.5 sizes below 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 8 (18.13 mm) and 0.41 mm narrower than a 9 (18.95 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 8½ by most of a size.

Size 8½ in the UK, Europe and Japan

A 8½ is 58.2 mm round. UK letters on the BS 6820 scale cover 0.625 mm each with half sizes, and Q½ runs from 57.81 to 58.44 mm, so a 8½ sits near the top of Q½. If you are on the large side of a 8½, a UK R may suit better.

ISO 8653 rounds to the nearest millimetre, so EU 58 covers 57.5 to 58.5 mm and a 8½ lands 0.74 mm into that band. Swiss and Italian sizes subtract 40, giving 18. Japan 18 is 18.7 mm inside, 0.16 mm larger than a US 8½, so Japanese 18 is the nearest match.

Quarter sizes either side

A 8¼ is 18.34 mm and a 8¾ is 18.74 mm, each about 0.2 mm from a 8½: roughly the thickness of two sheets of paper on the diameter. If your ring falls between 8¼ and 8¾ on the 1:1 circle, order a 8½ for a band under 4 mm.

For a 4–6 mm band, jewellers suggest 8¾ to 9; for 7 mm and wider, 9 to 9½; for a comfort-fit inside, 8 to 8¼. Smart-ring kits that include a size 9 sample: Oura Ring 4, Galaxy Ring, Ring AIR.

Making a size 8½ band

The blank length is the circumference of the middle of the band wall: π × (18.54 + thickness). Cut 63.0 mm of 1.5 mm stock or 64.5 mm of 2.0 mm stock, and the finished band has an outside diameter of 21.54 or 22.54 mm. Leave a little extra for filing the joint, and true the band on a mandrel at 8½ after soldering.

Blank = π × (18.54 mm + t) · 1.5 mm → 63.0 mm · 2.0 mm → 64.5 mm

Questions

Answered plainly.

01What is a size 8½ ring in mm?+

A US size 8½ ring is 18.54 mm (0.730") across the inside, with an inside circumference of 58.2 mm (2.29").

02What is a US size 8½ in UK and EU sizes?+

US 8½ is UK Q½ and EU (ISO 8653) 58. It is also Japan 18 and Swiss 18.

03How much bigger is a size 9 than a size 8½?+

A size 9 is 0.41 mm wider inside (18.95 against 18.54 mm) and 1.28 mm longer round.

04How long a blank do I cut for a size 8½ ring?+

63.0 mm for 1.5 mm thick stock and 64.5 mm for 2.0 mm, from π × (18.54 mm + thickness).

05Should I order a size 8½ for a wide band?+

For a band 7 mm or wider, jewellers suggest 9 to 9½; for 4–6 mm, 8¾ to 9. Under 4 mm, a 8½ fits true to size.

Ring sizesUS · inside Ø mm

Carat sizes

Necklace lengths