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US ring size 3½

A US size 3½ ring is 14.47 mm (0.570") across the inside and 45.5 mm (1.79") round. It converts to UK G½, EU 45, Japan 5 and Swiss 5.5. The 1:1 circle below is already set to size 3½: 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 3½14.47 mm · 0.570" inside · 45.5 mm round
Inside diameter14.47 mm
Band wall1.8 mm
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Full chart 19 rows

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Size 3½ and the quarter sizes around it

9 rows
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US ring size 3.5 and quarter sizes within one size either side: inside diameter, difference in mm, circumference, UK and EU sizes
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13.66−0.81 mm42.9E½43
13.87−0.61 mm43.6F44
14.07−0.41 mm44.2F½44
14.27−0.20 mm44.8G45
14.47—45.5G½45
14.68+0.20 mm46.1H46
14.88+0.41 mm46.8H½47
15.08+0.61 mm47.4I47
15.29+0.81 mm48.0I½48

Ordering a size 3½ in different band widths

4 rows
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What size to order for a US size 3.5 finger in narrow, 4–6 mm, 7 mm and wider, and comfort-fit bands
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3½14.47Bands under 4 mm usually fit true to size.
3¾–414.68–14.88A 4–6 mm band covers more skin and feels snugger: jewellers suggest a quarter to a half size up.
4–4½14.88–15.29Wide and cigar bands grip the whole finger segment: half a size to a full size up.
3–3¼14.07–14.27A domed comfort-fit inside slips over the knuckle more easily: often a quarter to a half size down.

Blank length for a size 3½ band

6 rows
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Length of wire or sheet to cut for a US size 3.5 ring band (14.47 mm inside) in stock 1.0 to 2.5 mm thick, by π × (inside diameter + thickness)
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48.61.914"16.47
49.21.939"16.87
50.21.976"17.47
51.12.013"18.07
51.82.038"18.47
53.32.100"19.47

05 / Field guide

Size 3½,
14.47 mm inside.

Everything about a US 3½: 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 3 and size 4.

Who wears a size 3½

A US 3½ is a petite size: little fingers, midi rings worn above the knuckle, and many teenagers. Jewellers’ order data puts the most common women’s size at 7 and men’s at 10, so a 3½ is 3.5 sizes below the usual women’s size and 6.5 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 3 (14.07 mm) and 0.41 mm narrower than a 4 (14.88 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 3½ by most of a size.

Size 3½ in the UK, Europe and Japan

A 3½ is 45.5 mm round. UK letters on the BS 6820 scale cover 0.625 mm each with half sizes, and G½ runs from 45.31 to 45.94 mm, so a 3½ sits near the bottom of G½. If you are on the small side of a 3½, a UK G may suit better.

ISO 8653 rounds to the nearest millimetre, so EU 45 covers 44.5 to 45.5 mm and a 3½ lands 0.97 mm into that band. Swiss and Italian sizes subtract 40, giving 5.5. Japan 5 is 14.3 mm inside, 0.17 mm smaller than a US 3½, so Japanese 5 is the nearest match.

Quarter sizes either side

A 3¼ is 14.27 mm and a 3¾ is 14.68 mm, each about 0.2 mm from a 3½: roughly the thickness of two sheets of paper on the diameter. If your ring falls between 3¼ and 3¾ on the 1:1 circle, order a 3½ for a band under 4 mm.

For a 4–6 mm band, jewellers suggest 3¾ to 4; for 7 mm and wider, 4 to 4½; for a comfort-fit inside, 3 to 3¼. No current smart ring comes in this size.

Making a size 3½ band

The blank length is the circumference of the middle of the band wall: π × (14.47 + thickness). Cut 50.2 mm of 1.5 mm stock or 51.8 mm of 2.0 mm stock, and the finished band has an outside diameter of 17.47 or 18.47 mm. Leave a little extra for filing the joint, and true the band on a mandrel at 3½ after soldering.

Blank = π × (14.47 mm + t) · 1.5 mm → 50.2 mm · 2.0 mm → 51.8 mm

Questions

Answered plainly.

01What is a size 3½ ring in mm?+

A US size 3½ ring is 14.47 mm (0.570") across the inside, with an inside circumference of 45.5 mm (1.79").

02What is a US size 3½ in UK and EU sizes?+

US 3½ is UK G½ and EU (ISO 8653) 45. It is also Japan 5 and Swiss 5.5.

03How much bigger is a size 4 than a size 3½?+

A size 4 is 0.41 mm wider inside (14.88 against 14.47 mm) and 1.28 mm longer round.

04How long a blank do I cut for a size 3½ ring?+

50.2 mm for 1.5 mm thick stock and 51.8 mm for 2.0 mm, from π × (14.47 mm + thickness).

05Should I order a size 3½ for a wide band?+

For a band 7 mm or wider, jewellers suggest 4 to 4½; for 4–6 mm, 3¾ to 4. Under 4 mm, a 3½ fits true to size.

Ring sizesUS · inside Ø mm

Carat sizes

Necklace lengths