How to measure your ring size

At NOOI we make every ring in a US size, converted from inner diameter — the most accurate way to convert a ring size. A digital caliper on a ring that already fits is the method we trust.

If you know your ring size, but it isn’t listed in US sizing—and you’re not familiar with how ring sizes convert—feel free to contact us.

Ring size converter

Use one field, then convert. The tool picks the nearest US size on the chart, including quarter sizes (¼, ½, ¾).

Ring size chart

Inner diameter and circumference in millimetres. Shop size = United States (also Canada and Mexico). Convert highlights the row and circles the US size.

Ø mm Circ. mm US UK East Asia India IT / ES / NL / CH
11.63 36.5 0 — — — —
11.84 37.2 ¼ — — — —
12.04 37.8 ½ A — — —
12.24 38.5 ¾ A½ — — —
12.45 39.1 1 B 1 — —
12.65 39.7 1¼ B½ — — —
12.85 40.4 1½ C — — 0.4
13.06 41.0 1¾ C½ — — —
13.26 41.7 2 D — — —
13.46 42.3 2¼ D½ — — —
13.67 42.9 2½ E — — —
13.87 43.6 2¾ E½ — — —
14.07 44.2 3 F 4 — 4.2
14.27 44.8 3¼ F½ 5 5 4.8
14.48 45.5 3½ G — — 5.5
14.68 46.1 3¾ G½ 6 6 6.1
14.88 46.8 4 H 7 — 6.8
15.09 47.4 4¼ H½ — 7 7.4
15.29 48.0 4½ I 8 8 8
15.49 48.7 4¾ J — 9 8.7
15.70 49.3 5 J½ 9 — 9.3
15.90 50.0 5¼ K — 10 10
16.10 50.6 5½ K½ 10 — 10.6
16.31 51.2 5¾ L — 11 11.2
16.51 51.9 6 L½ 11 12 11.9
16.71 52.5 6¼ M 12 — 12.5
16.92 53.1 6½ M½ 13 13 13.1
17.12 53.8 6¾ N — — 13.8
17.32 54.4 7 N½ 14 14 14.4
17.53 55.1 7¼ O — 15 15.1
17.73 55.7 7½ O½ 15 — 15.7
17.93 56.3 7¾ P — 16 16.3
18.14 57.0 8 P½ 16 17 17
18.34 57.6 8¼ P¾ — — 17.6
18.54 58.3 8½ Q¼ 17 18 18.3
18.75 58.9 8¾ R — 19 18.9
18.95 59.5 9 R½ 18 — 19.5
19.15 60.2 9¼ S — 20 20.2
19.35 60.8 9½ S½ 19 21 20.8
19.56 61.4 9¾ T — — 21.4
19.76 62.1 10 T½ 20 22 22.1
19.96 62.7 10¼ U 21 23 22.7
20.17 63.4 10½ U½ 22 — 23.4
20.37 64.0 10¾ V — 24 24
20.57 64.6 11 V½ 23 25 24.6
20.78 65.3 11¼ W — — 25.3
20.98 65.9 11½ W½ 24 26 25.9
21.18 66.6 11¾ X — — 26.6
21.39 67.2 12 X½ 25 27 27.2
21.59 67.8 12¼ Y — 28 27.8
21.79 68.5 12½ Y½ 26 — 28.5
22.00 69.1 12¾ Z — 29 29.1
22.20 69.7 13 Z½ 27 30 29.7
22.40 70.4 13¼ Z1 — — 30.4
22.61 71.0 13½ — — 31 31
22.81 71.7 13¾ Z2 — 32 31.7
23.01 72.3 14 Z3 — — 32.3
23.22 72.9 14¼ — — 33 32.9
23.42 73.6 14½ Z4 — — 33.6
23.62 74.2 14¾ — — 34 34.2
23.83 74.8 15 — — 35 34.8
24.03 75.5 15¼ — — — 35.5
24.23 76.1 15½ — — 36 36.1
24.43 76.8 15¾ — — — 36.8
24.64 77.4 16 — — 37 37.4

After you order

At checkout, pick the closest US size. If you are not entirely certain, feel free to email us the inner diameter in millimetres. We will make the ring to that diameter.

How to measure the inner diameter

  1. Take a ring that already sits well on the intended finger.
  2. Measure the inside diameter with a digital caliper, in millimetres, straight across the centre (to be more accurate, measure in a few spots).
  3. Choose the matching US size so you can check out, then email us that same millimetre figure after the order.

Do not wrap string or paper around the finger. That gives a circumference, not the inner diameter we make to.

Convert inner diameter to US ring size

Measure the inside of a ring that fits, in millimetres, then convert. On the NOOI chart: 16.51 mm = US 6, 17.32 mm = US 7, 18.14 mm = US 8.

Convert inner circumference to US ring size

Inner circumference in millimetres is the EU / ISO size. On the NOOI chart: 51.9 mm = US 6, 54.4 mm = US 7, 57.0 mm = US 8.

Convert UK letter to US ring size

On the NOOI chart: L½ = US 6, N½ = US 7, P½ = US 8.

Convert Italian size to US ring size

Italian size is also used in Spain, the Netherlands and Switzerland — not Japan. On the NOOI chart: 11.9 = US 6, 13.8 = US 6¾, 14.4 = US 7.

Common conversions (NOOI chart)

You have US size
16.51 mm inner diameter 6
17.32 mm inner diameter 7
18.14 mm inner diameter 8
51.9 mm inner circumference 6
54.4 mm inner circumference 7
57.0 mm inner circumference 8
UK L½ 6
UK N½ 7
Italian 11.9 6
Italian 13.8 6¾
Japanese 11 6

Ring size questions

What US ring size is 16.51 mm inner diameter?
US 6 on the NOOI chart (UK L½, Italian 11.9).
What US ring size is 54.4 mm inner circumference?
US 7. EU / ISO size is this circumference in millimetres.
What US size is UK L½?
US 6.
What US size is Italian 13.8?
US 6¾ (17.12 mm inner diameter).
Is Italian ring size the same as Japanese?
No. US 6 is Italian 11.9 and Japanese 11. The Japanese column is East Asia, not the Italian scale.

All set with your size? Start planning your engagement ring with NOOI.

Handmade in Italy in 18k gold — each ring is made to the US size you converted. Click a card to open that collection.

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