Skip to content
SizeCheck
EN

US ring size chart, with quarter sizes

Every US and Canadian ring size from 3 to 13 in quarter steps, with the inside diameter and circumference in millimetres and inches, and UK and EU equivalents.

US ring size chart, 3 to 13 in quarter sizes
US & CanadaDiameter mmDiameter inDiameter in (approx.)Circumference mmCircumference inUK & AustraliaEU / ISO
314.10.5549/16"44.21.74F½44
3¼14.30.5629/16"44.81.77G45
3½14.50.5709/16"45.51.79G½45
3¾14.70.5789/16"46.11.82H46
414.90.5869/16"46.81.84H½47
4¼15.10.5945/8"47.41.87I47
4½15.30.6025/8"48.01.89I½48
4¾15.50.6105/8"48.71.92J49
515.70.6185/8"49.31.94J½49
5¼15.90.6265/8"50.01.97K50
5½16.10.6345/8"50.61.99K½51
5¾16.30.6425/8"51.22.02L51
616.50.6505/8"51.92.04L½52
6¼16.70.65811/16"52.52.07M53
6½16.90.66611/16"53.12.09M½53
6¾17.10.67411/16"53.82.12N54
717.30.68211/16"54.42.14N½54
7¼17.50.69011/16"55.12.17O55
7½17.70.69811/16"55.72.19O½56
7¾17.90.70611/16"56.32.22P56
818.10.71411/16"57.02.24P½57
8¼18.30.7223/4"57.62.27Q58
8½18.50.7303/4"58.32.29Q½58
8¾18.70.7383/4"58.92.32R59
918.90.7463/4"59.52.34R½60
9¼19.20.7543/4"60.22.37S60
9½19.40.7623/4"60.82.39S½61
9¾19.60.7703/4"61.42.42T61
1019.80.7783/4"62.12.44T½62
10¼20.00.78613/16"62.72.47U63
10½20.20.79413/16"63.42.49U½63
10¾20.40.80213/16"64.02.52V64
1120.60.81013/16"64.62.54V½65
11¼20.80.81813/16"65.32.57W65
11½21.00.82613/16"65.92.59W½66
11¾21.20.83413/16"66.62.62X67
1221.40.84213/16"67.22.65Y67
12¼21.60.8507/8"67.82.67Y½68
12½21.80.8587/8"68.52.70Z68
12¾22.00.8667/8"69.12.72Z½69
1322.20.8747/8"69.72.75Z+170

Whole sizes in darker text. The inch fraction is rounded to the nearest 1/16 inch, as a ruler shows it; use the decimal for anything precise.

The formula behind US ring sizes

US ring sizes are an inch scale based on the ring's inside diameter:

inside diameter (in) = 0.458 + 0.032 × size

In millimetres that is 11.63 + 0.8128 × size, and around the inside it is about 36.5 + 2.55 × size mm. Every whole size adds 0.81 mm across, every half size 0.41 mm, and every quarter size 0.2 mm. That is why accurate measuring matters: a quarter size is thinner than a credit card.

Measuring for a US size at home

  • Ruler and a ring: measure straight across the inside of a ring that fits, in mm, and find it in the diameter column.
  • On screen: calibrate your screen with a bank card and match the ring on the on-screen sizer. It shows quarter sizes.
  • On paper: the printable ring sizer prints on US Letter and checks your printer is at 100%.
  • String or strip: measure around your finger in inches and use the inches to ring size converter.

Canada and Mexico

Canada and Mexico use the same sizes as the United States, so this chart works for all three. For UK, European, Japanese or other sizes, see the full international ring size chart.

Common questions

How are US ring sizes defined?
By inside diameter. Size 0 is 0.458 inch across, and each whole size adds 0.032 inch (0.81 mm). So a size 7 is 0.458 + 7 × 0.032 = 0.682 inch, or 17.32 mm. Canada and Mexico use the same scale.
What is the difference between a half size and a quarter size?
A half size is 0.4 mm of diameter, a quarter size 0.2 mm. Quarter sizes matter most for wide bands and for people between sizes. Many shops sell half sizes only; some fine jewellers make quarter sizes on request.
What size is 17 mm in US ring size?
A ring 17 mm across the inside is US 6.6, so about a 6½. 18 mm is US 7.8 (about 7¾), and 16 mm is US 5.4 (between 5¼ and 5½). Use the converter for any other value.
Do US ring sizes differ between brands?
They should not, but real rings vary slightly: different mandrels, finishing, and band widths. A size 7 in a thin band and a size 7 in a wide band will feel different. The numbers on this chart are the standard dimensions.

Next