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US ring size 5½

A US size 5½ ring is 16.10 mm (0.634") across the inside and 50.6 mm (1.99") round. It converts to UK K½, EU 51, Japan 10 and Swiss 10.5. The 1:1 circle below is already set to size 5½: 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 5½16.10 mm · 0.634" inside · 50.6 mm round
Inside diameter16.10 mm
Band wall1.8 mm
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Full chart 19 rows

Sort any column, download it as CSV or print it. Click a row to show it at 1:1.

Size 5½ and the quarter sizes around it

9 rows
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US ring size 5.5 and quarter sizes within one size either side: inside diameter, difference in mm, circumference, UK and EU sizes
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15.29−0.81 mm48.0I½48
15.49−0.61 mm48.7J49
15.69−0.41 mm49.3J½49
15.90−0.20 mm49.9K50
16.10—50.6K½51
16.30+0.20 mm51.2L51
16.51+0.41 mm51.9L½52
16.71+0.61 mm52.5M52
16.91+0.81 mm53.1M½53

Ordering a size 5½ in different band widths

4 rows
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What size to order for a US size 5.5 finger in narrow, 4–6 mm, 7 mm and wider, and comfort-fit bands
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5½16.10Bands under 4 mm usually fit true to size.
5¾–616.30–16.51A 4–6 mm band covers more skin and feels snugger: jewellers suggest a quarter to a half size up.
6–6½16.51–16.91Wide and cigar bands grip the whole finger segment: half a size to a full size up.
5–5¼15.69–15.90A domed comfort-fit inside slips over the knuckle more easily: often a quarter to a half size down.

Blank length for a size 5½ band

6 rows
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Length of wire or sheet to cut for a US size 5.5 ring band (16.10 mm inside) in stock 1.0 to 2.5 mm thick, by π × (inside diameter + thickness)
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53.72.115"18.10
54.42.140"18.50
55.32.177"19.10
56.22.214"19.70
56.92.239"20.10
58.42.301"21.10

05 / Field guide

Size 5½,
16.10 mm inside.

Everything about a US 5½: 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 5 and size 6.

Who wears a size 5½

A US 5½ is a smaller women’s size, below the 6 to 8½ range most women wear, and a common pinky size for men. Jewellers’ order data puts the most common women’s size at 7 and men’s at 10, so a 5½ is 1.5 sizes below the usual women’s size and 4.5 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 5 (15.69 mm) and 0.41 mm narrower than a 6 (16.51 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 5½ by most of a size.

Size 5½ in the UK, Europe and Japan

A 5½ is 50.6 mm round. UK letters on the BS 6820 scale cover 0.625 mm each with half sizes, and K½ runs from 50.31 to 50.94 mm, so a 5½ sits in the middle of K½. It converts cleanly, so a UK K½ ring should feel the same.

ISO 8653 rounds to the nearest millimetre, so EU 51 covers 50.5 to 51.5 mm and a 5½ lands 0.08 mm into that band. Swiss and Italian sizes subtract 40, giving 10.5. Japan 10 is 16.0 mm inside, 0.10 mm smaller than a US 5½, so Japanese 10 is the nearest match.

Quarter sizes either side

A 5¼ is 15.90 mm and a 5¾ is 16.30 mm, each about 0.2 mm from a 5½: roughly the thickness of two sheets of paper on the diameter. If your ring falls between 5¼ and 5¾ on the 1:1 circle, order a 5½ for a band under 4 mm.

For a 4–6 mm band, jewellers suggest 5¾ to 6; for 7 mm and wider, 6 to 6½; for a comfort-fit inside, 5 to 5¼. Smart-ring kits that include a size 6 sample: Oura Ring 4, Galaxy Ring, Ring AIR.

Making a size 5½ band

The blank length is the circumference of the middle of the band wall: π × (16.10 + thickness). Cut 55.3 mm of 1.5 mm stock or 56.9 mm of 2.0 mm stock, and the finished band has an outside diameter of 19.10 or 20.10 mm. Leave a little extra for filing the joint, and true the band on a mandrel at 5½ after soldering.

Blank = π × (16.10 mm + t) · 1.5 mm → 55.3 mm · 2.0 mm → 56.9 mm

Questions

Answered plainly.

01What is a size 5½ ring in mm?+

A US size 5½ ring is 16.10 mm (0.634") across the inside, with an inside circumference of 50.6 mm (1.99").

02What is a US size 5½ in UK and EU sizes?+

US 5½ is UK K½ and EU (ISO 8653) 51. It is also Japan 10 and Swiss 10.5.

03How much bigger is a size 6 than a size 5½?+

A size 6 is 0.41 mm wider inside (16.51 against 16.10 mm) and 1.28 mm longer round.

04How long a blank do I cut for a size 5½ ring?+

55.3 mm for 1.5 mm thick stock and 56.9 mm for 2.0 mm, from π × (16.10 mm + thickness).

05Should I order a size 5½ for a wide band?+

For a band 7 mm or wider, jewellers suggest 6 to 6½; for 4–6 mm, 5¾ to 6. Under 4 mm, a 5½ fits true to size.

Ring sizesUS · inside Ø mm

Carat sizes

Necklace lengths