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US ring size 7½

A US size 7½ ring is 17.73 mm (0.698") across the inside and 55.7 mm (2.19") round. It converts to UK O½, EU 56, Japan 15 and Swiss 15.5. The 1:1 circle below is already set to size 7½: 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 7½17.73 mm · 0.698" inside · 55.7 mm round
Inside diameter17.73 mm
Band wall1.8 mm
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Full chart 19 rows

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Size 7½ and the quarter sizes around it

9 rows
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US ring size 7.5 and quarter sizes within one size either side: inside diameter, difference in mm, circumference, UK and EU sizes
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16.91−0.81 mm53.1M½53
17.12−0.61 mm53.8N54
17.32−0.41 mm54.4N½54
17.52−0.20 mm55.0O55
17.73—55.7O½56
17.93+0.20 mm56.3P56
18.13+0.41 mm57.0P½57
18.34+0.61 mm57.6Q58
18.54+0.81 mm58.2Q½58

Ordering a size 7½ in different band widths

4 rows
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What size to order for a US size 7.5 finger in narrow, 4–6 mm, 7 mm and wider, and comfort-fit bands
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7½17.73Bands under 4 mm usually fit true to size.
7¾–817.93–18.13A 4–6 mm band covers more skin and feels snugger: jewellers suggest a quarter to a half size up.
8–8½18.13–18.54Wide and cigar bands grip the whole finger segment: half a size to a full size up.
7–7¼17.32–17.52A domed comfort-fit inside slips over the knuckle more easily: often a quarter to a half size down.

Blank length for a size 7½ band

6 rows
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Length of wire or sheet to cut for a US size 7.5 ring band (17.73 mm inside) in stock 1.0 to 2.5 mm thick, by π × (inside diameter + thickness)
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58.82.316"19.73
59.52.341"20.13
60.42.378"20.73
61.32.415"21.33
62.02.440"21.73
63.52.502"22.73

05 / Field guide

Size 7½,
17.73 mm inside.

Everything about a US 7½: 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 7 and size 8.

Who wears a size 7½

A US 7½ 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 7½ is 0.5 sizes above the usual women’s size and 2.5 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 7 (17.32 mm) and 0.41 mm narrower than a 8 (18.13 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 7½ by most of a size.

Size 7½ in the UK, Europe and Japan

A 7½ is 55.7 mm round. UK letters on the BS 6820 scale cover 0.625 mm each with half sizes, and O½ runs from 55.31 to 55.94 mm, so a 7½ sits in the middle of O½. It converts cleanly, so a UK O½ ring should feel the same.

ISO 8653 rounds to the nearest millimetre, so EU 56 covers 55.5 to 56.5 mm and a 7½ lands 0.19 mm into that band. Swiss and Italian sizes subtract 40, giving 15.5. Japan 15 is 17.7 mm inside, 0.03 mm smaller than a US 7½, so Japanese 15 is the nearest match.

Quarter sizes either side

A 7¼ is 17.52 mm and a 7¾ is 17.93 mm, each about 0.2 mm from a 7½: roughly the thickness of two sheets of paper on the diameter. If your ring falls between 7¼ and 7¾ on the 1:1 circle, order a 7½ for a band under 4 mm.

For a 4–6 mm band, jewellers suggest 7¾ to 8; for 7 mm and wider, 8 to 8½; for a comfort-fit inside, 7 to 7¼. Smart-ring kits that include a size 8 sample: Oura Ring 4, Galaxy Ring, Ring AIR.

Making a size 7½ band

The blank length is the circumference of the middle of the band wall: π × (17.73 + thickness). Cut 60.4 mm of 1.5 mm stock or 62.0 mm of 2.0 mm stock, and the finished band has an outside diameter of 20.73 or 21.73 mm. Leave a little extra for filing the joint, and true the band on a mandrel at 7½ after soldering.

Blank = π × (17.73 mm + t) · 1.5 mm → 60.4 mm · 2.0 mm → 62.0 mm

Questions

Answered plainly.

01What is a size 7½ ring in mm?+

A US size 7½ ring is 17.73 mm (0.698") across the inside, with an inside circumference of 55.7 mm (2.19").

02What is a US size 7½ in UK and EU sizes?+

US 7½ is UK O½ and EU (ISO 8653) 56. It is also Japan 15 and Swiss 15.5.

03How much bigger is a size 8 than a size 7½?+

A size 8 is 0.41 mm wider inside (18.13 against 17.73 mm) and 1.28 mm longer round.

04How long a blank do I cut for a size 7½ ring?+

60.4 mm for 1.5 mm thick stock and 62.0 mm for 2.0 mm, from π × (17.73 mm + thickness).

05Should I order a size 7½ for a wide band?+

For a band 7 mm or wider, jewellers suggest 8 to 8½; for 4–6 mm, 7¾ to 8. Under 4 mm, a 7½ fits true to size.

Ring sizesUS · inside Ø mm

Carat sizes

Necklace lengths