UK, US, EU and millimetres

UK ring size conversion chart

Each row keeps a UK letter with inside diameter, circumference, US size and EU size. Send the millimetres and the name of the chart, because another published chart, including GIA, can pair the same letter with a different opening.
Read the ring sizing guide Ask us about a measurement

USING THE CHART

How to read this chart

How the rows work, where the figures come from, and how to measure so you pick the right row.

HOW TO READ THE CHART

One row per size, with anchors

Find a UK letter, a millimetre measurement or a US size, then read every label on that same row.

The full table below gives every size on this page, with a row anchor for each UK letter, diameter, circumference and first occurrence of a US size. Examples: UK J, UK L, UK M, UK N, 17.3 mm diameter, 54.4 mm circumference, US 7.

This page does not offer a downloadable PDF. The conversion chart is published here, and the same rows appear on our ring sizing guide, which also covers how to measure.

SOURCES

Where these figures come from

Millimetres are the anchor. UK and US labels are the labels on this named chart, not a universal conversion.

EU size on this page follows inner circumference in millimetres, rounded to the nearest whole number, which is the usual way ISO 8653 ring size designation is presented to consumers (see the ISO 8653:2016 abstract).

The UK letter, diameter, circumference and US pairings are the same rows used on our ring sizing guide. They align with a published UK jeweller conversion table. They do not always match the GIA international chart. GIA lists 16.1 mm and 50.6 mm as US 5½ and UK K, and 17.7 mm and 55.6 mm as US 7½ and UK O (see GIA on finger and ring size). On this chart those letters sit on different millimetre rows, which is why you should send the millimetres and the chart name.

MEASURING

Measure in millimetres, then choose the row

The ring must be round before you use an inside diameter. Band width also changes how a size feels.

If you have a ring that already fits the same finger, measure the inner diameter in millimetres across the opening, then find that diameter on this chart. GIA advises that the inside must be perfectly round before you size from diameter, and that wider bands can feel tighter than a narrow ring of the same letter.

Our ring sizing guide explains how we confirm a size before a ring is made, and how a free resize within 1 month of delivery works, through a local jeweller, with evidence, where the design allows it.

Book a free consultation

UK, US, EU and millimetre conversion chart

Read the inside measurement in millimetres, then use every label on that same row. UK letters on this chart are not circumference values. ISO 8653 defines ring size designation with a specified ring stick, and EU size here follows inner circumference to the nearest millimetre. GIA can pair the same letter with a different opening, so keep the millimetres and the chart name together. The same rows are used on our ring sizing guide.

On this chart, 17.3 mm inside diameter is listed as 54.4 mm circumference, UK N½ and US 7. Diameter times π (3.1416) is about 54.3 mm, which is the circumference GIA lists for US 7 and UK N. Here, 17.4 mm is UK O and US 7.25, and 17.7 mm is UK O½ and US 7.5. GIA pairs 17.7 mm and 55.6 mm with UK O and US 7½. Jump to a letter with the anchors, for example UK L, UK N½ or UK O.

UK letter, millimetres and US size

A short extract of common UK letters, using the same rows as the full chart below. Each letter links to its row.

Compact UK letter, millimetre and US ring size table for sizes J to T.
UK Diameter mm Circumference mm US
J 15.4 48.4 4.75
J½ 15.6 49.0 5
K 15.8 49.6 5.25
K½ 16.0 50.3 5.5
L 16.2 51.0 5.75
L½ 16.4 51.5 6
M 16.6 52.2 6.25
M½ 16.8 52.8 6.5
N 17.0 53.4 6.75
N½ 17.2 54.1 7
O 17.4 54.7 7.25
O½ 17.6 55.3 7.5
P 17.8 55.9 7.75
P½ 18.0 56.6 8
Q 18.2 57.2 8.25
Q½ 18.4 57.8 8.5
R 18.6 58.4 8.75
R½ 18.8 59.1 9
S 19.1 60.0 9.25
S½ 19.3 60.6 9.5
T 19.5 61.3 9.75

This is a short extract of the chart below, using the same rows. The full table includes every size on this page, with EU sizes and row anchors.

Show alongside UK:
International ring size conversion chart showing UK, EU/ISO, US/Canada, Asia, Italy/Spain and German ring sizes, with inner circumference and diameter in millimetres.
Circum.mm Diametermm EU / ISOFrance / Europe US / CAUSA & Canada UK / AUUnited Kingdom Italy / SpainEU size - 40 AsiaJP / CN / SG / HK Germandiameter mm
44.0 14.0 44 2.75 F 4 4 14
44.3 14.1 44 3 F½ 4 4 14
44.6 14.2 45 3.25 G 5 14
44.9 14.3 45 3.25 G 5 5 14
45.2 14.4 45 3.5 G½ 5 5 14
45.6 14.5 46 3.5 G½ 6 15
46.2 14.7 46 3.75 H 6 6 15
46.5 14.8 47 4 H½ 7 15
46.8 14.9 47 4 H½ 7 7 15
47.1 15.0 47 4.25 I 7 15
47.4 15.1 47 4.25 I 7 8 15
47.8 15.2 48 4.5 I½ 8 8 15
48.0 15.3 48 4.5 I½ 8 15
48.4 15.4 48 4.75 J 8 9 15
48.7 15.5 49 4.75 J 9 9 16
49.0 15.6 49 5 J½ 9 16
49.3 15.7 49 5 J½ 9 16
49.6 15.8 50 5.25 K 10 10 16
50.0 15.9 50 5.25 K 10 10 16
50.3 16.0 50 5.5 K½ 10 16
50.6 16.1 51 5.5 K½ 11 16
51.0 16.2 51 5.75 L 11 16
51.2 16.3 51 5.75 L 11 11 16
51.5 16.4 52 6 L½ 12 11 16
51.8 16.5 52 6 L½ 12 17
52.2 16.6 52 6.25 M 12 17
52.5 16.7 53 6.25 M 13 12 17
52.8 16.8 53 6.5 M½ 13 12 17
53.1 16.9 53 6.5 M½ 13 17
53.4 17.0 53 6.75 N 13 17
53.8 17.1 54 6.75 N 14 13 17
54.1 17.2 54 7 N½ 14 13 17
54.4 17.3 54 7 N½ 14 17
54.7 17.4 55 7.25 O 15 17
55.0 17.5 55 7.25 O 15 18
55.3 17.6 55 7.5 O½ 15 14 18
55.6 17.7 56 7.5 O½ 16 14 18
55.9 17.8 56 7.75 P 16 18
56.2 17.9 56 7.75 P 16 18
56.6 18.0 57 8 P½ 17 15 18
56.9 18.1 57 8 P½ 17 15 18
57.2 18.2 57 8.25 Q 17 18
57.5 18.3 58 8.25 Q 18 18
57.8 18.4 58 8.5 Q½ 18 15 18
58.1 18.5 58 8.5 Q½ 18 18
58.4 18.6 58 8.75 R 18 16 18
58.8 18.7 59 8.75 R 19 16 19
59.1 18.8 59 9 R½ 19 19
59.4 18.9 59 9 R½ 19 19
59.7 19.0 60 9 R½ 20 17 19
60.0 19.1 60 9.25 S 20 17 19
60.3 19.2 60 9.25 S 20 19
60.6 19.3 61 9.5 S½ 21 19
60.9 19.4 61 9.5 S½ 21 18 19
61.3 19.5 61 9.75 T 21 18 19
61.6 19.6 62 9.75 T 22 20
61.9 19.7 62 10 T½ 22 20
62.2 19.8 62 10 T½ 22 19 20
62.5 19.9 63 10.25 U 23 20
62.8 20.0 63 10.25 U 23 20
63.2 20.1 63 10.5 U½ 23 19 20
63.5 20.2 64 10.5 U½ 24 20 20
63.8 20.3 64 10.75 V 24 20
64.1 20.4 64 10.75 V½ 24 20
64.4 20.5 64 11 V½ 24 21 20
64.7 20.6 65 11 W 25 20
65.1 20.7 65 11.25 W 25 21
65.4 20.8 65 11.25 W½ 25 22 21
65.7 20.9 66 11.5 W½ 26 22 21
66.0 21.0 66 11.5 X 26 21
66.3 21.1 66 11.75 X 26 21
66.6 21.2 67 11.75 X½ 27 23 21
66.9 21.3 67 12 X½ 27 21
67.2 21.4 67 12 Y 27 21
67.5 21.5 68 12.25 Y 28 24 21
67.9 21.6 68 12.25 Y½ 28 22
68.2 21.7 68 12.5 Z 28 22
68.5 21.8 69 12.5 Z 29 25 22
68.8 21.9 69 12.75 Z½ 29 22
69.1 22.0 69 12.75 Z+1 29 22
69.4 22.1 69 13 Z+1 29 26 22
69.7 22.2 70 13 Z+1½ 30 26 22
70.1 22.3 70 13.25 Z+2 30 22
70.4 22.4 70 13.25 Z+2 30 22
70.7 22.5 71 13.5 Z+2½ 31 27 23
71.0 22.6 71 13.5 Z+3 31 23

EU / ISO and French sizing: the EU/ISO size is the inner circumference of the ring in millimetres, rounded to the nearest whole number.

Italy / Spain sizing: this column uses the common Italy and Spain conversion of EU/ISO size minus 40. For example, EU 54 converts to Italy / Spain size 14.

German sizing: this column is a rounded diameter reference. Use the exact diameter column for the most precise measurement.

Not sure which row applies? Send the measurement in millimetres, the chart or gauge you used, and the band width. We will sense check it before anything is made. The chart is on this page. We do not offer a downloadable PDF.

Ask us about a measurement

Related guides

Ring sizing and the rings we make

Use this chart with our ring sizing guide. If you are commissioning a ring, start with the design page or a consultation.

Guide

Ring sizing guide

How to measure, how charts can disagree, and how we confirm a size before making begins.

Read the ring sizing guide

Design

Design your engagement ring

A bespoke engagement ring, designed around your brief. Pieces start from £600.

Design your ring

Bands

Wedding bands

Plain, diamond set, shaped and fitted wedding bands, planned to sit with an engagement ring.

View wedding bands

Fit

Flush engagement rings

Engagement ring profiles designed so a wedding band can sit close beside them.

View flush fit rings

Help

Ask about a measurement

Send the millimetres, the chart or gauge you used, and the band width, and we will sense check it.

Contact us

Why charts disagree

The same UK letter is not always the same opening

Use millimetres as the anchor, and name the chart. The examples below are the documented differences we have checked.

Letters on these rows

This page's UK chart

UK letters, US sizes, diameters and circumferences on this page follow the same rows as our ring sizing guide, and align with a published UK jeweller table.

Wearability High

Use these labels only with this chart's millimetres.

A different opening for the same letter

GIA published pairing

GIA lists UK K with 16.1 mm and 50.6 mm (US 5½), and UK O with 17.7 mm and 55.6 mm (US 7½). Those letters sit on different millimetre rows here.

Wearability High

Do not mix a GIA letter with this chart's millimetres.

Circumference in millimetres

EU and ISO

EU size on this page is the inner circumference in millimetres, rounded to the nearest whole number, in line with how ISO 8653 designation is usually shown.

Wearability High

A circumference in millimetres is the most portable figure.

Millimetres and the chart name

What to send us

Send the inside diameter or circumference in millimetres, the name of the chart or gauge, and the intended band width. We will sense check it before anything is made.

Wearability High

A letter on its own is not enough when charts disagree.

Letters on these rows

This page's UK chart

UK letters, US sizes, diameters and circumferences on this page follow the same rows as our ring sizing guide, and align with a published UK jeweller table.

Wearability High

Use these labels only with this chart's millimetres.

A different opening for the same letter

GIA published pairing

GIA lists UK K with 16.1 mm and 50.6 mm (US 5½), and UK O with 17.7 mm and 55.6 mm (US 7½). Those letters sit on different millimetre rows here.

Wearability High

Do not mix a GIA letter with this chart's millimetres.

Circumference in millimetres

EU and ISO

EU size on this page is the inner circumference in millimetres, rounded to the nearest whole number, in line with how ISO 8653 designation is usually shown.

Wearability High

A circumference in millimetres is the most portable figure.

Millimetres and the chart name

What to send us

Send the inside diameter or circumference in millimetres, the name of the chart or gauge, and the intended band width. We will sense check it before anything is made.

Wearability High

A letter on its own is not enough when charts disagree.

Anchor figure

Inside diameter or circumference in mm

Millimetres as GIA lists them

Inner circumference to the nearest mm

Millimetres plus the chart name

UK O example

17.4 mm diameter, US 7.25

17.7 mm diameter, 55.6 mm, US 7½

Not a letter system

Send the millimetres, not only the letter

UK letters

Yes, on every row

Yes, on GIA's own rows

No

Name the chart the letter came from

Mixing with other charts

Do not mix rows

Do not mix with this chart

Works across countries

We check before making

Best used for

Reading a size from our ring sizing guide

Comparing with a GIA reference

Sizes from Europe and many online shops

Confirming a size with us

Band width

Wider bands can feel tighter

Same applies

Same applies

Tell us the intended width

Anchor figure

Inside diameter or circumference in mm

Millimetres as GIA lists them

Inner circumference to the nearest mm

Millimetres plus the chart name

UK O example

17.4 mm diameter, US 7.25

17.7 mm diameter, 55.6 mm, US 7½

Not a letter system

Send the millimetres, not only the letter

UK letters

Yes, on every row

Yes, on GIA's own rows

No

Name the chart the letter came from

Mixing with other charts

Do not mix rows

Do not mix with this chart

Works across countries

We check before making

Best used for

Reading a size from our ring sizing guide

Comparing with a GIA reference

Sizes from Europe and many online shops

Confirming a size with us

Band width

Wider bands can feel tighter

Same applies

Same applies

Tell us the intended width

The bottom line

Use this page's rows when you are reading a size from our ring sizing guide, and keep every label on the same row together.

If your size came from a GIA or another published chart, send the millimetres and the chart name rather than the letter alone.

Millimetres are the most reliable figure to send. We sense check every size before anything is made.

Not sure which row applies? Send the millimetres, the chart you used and the band width, and we will check them before anything is made.

Talk to us

USING THE CHART

How to use each column

Every label on a row belongs together. Do not mix a letter from one chart with millimetres from another.

UK letter

Available

A British letter size. It only describes the opening on this named chart.

Diameter in mm

Available

The inside diameter of a round ring, in millimetres. The ring must be round before you use this column.

Circumference in mm

Available

The inside circumference in millimetres. EU size on this page is that figure, rounded to the nearest whole number.

US size

Available

The US label on the same row of this chart, not a letter converted through a different table.

Row anchors

Available

Each size has an on-page anchor, so you can link to a letter or a millimetre row. There is no downloadable PDF.

Band width

Partial

A wider band can feel tighter than a narrow ring of the same letter. Tell us the intended width when you write.

UK letter Available

A British letter size. It only describes the opening on this named chart.

Diameter in mm Available

The inside diameter of a round ring, in millimetres. The ring must be round before you use this column.

Circumference in mm Available

The inside circumference in millimetres. EU size on this page is that figure, rounded to the nearest whole number.

US size Available

The US label on the same row of this chart, not a letter converted through a different table.

Row anchors Available

Each size has an on-page anchor, so you can link to a letter or a millimetre row. There is no downloadable PDF.

Band width Partial

A wider band can feel tighter than a narrow ring of the same letter. Tell us the intended width when you write.

Getting the size right

A bespoke ring, sized before it is made. Pieces start from £600

We confirm your size before production begins. Nothing is made until you approve the design.

Measure

Step 1

Use this chart and our ring sizing guide, then send the millimetres, the chart or gauge, and the band width.

Millimetres firstNamed chart

Confirm

Step 2

We sense check the measurement against the design, including band width, before making begins.

Checked before makingWritten approval

After delivery

Step 3

For resizable designs, we include one free resize within 1 month of delivery, through a local jeweller, with evidence.

Where the design allowsSee aftercare terms

UK letters, US sizes, EU sizes and millimetres.

Common questions about UK ring size conversion

The figures below follow this page's chart. Other charts can disagree, so keep the millimetres and the chart name together.

Find the UK letter in the table, then read the US size on that same row. Do not convert a letter from a different chart. You can jump to letters such as UK L or UK O.

On this chart, 17.3 mm inside diameter is listed as 54.4 mm circumference, UK N½ and US 7. GIA lists a circumference of about 54.3 mm as US 7 and UK N, so name the chart when you write to us. Jump to 17.3 mm.

Published tables can pair the same UK letter with a different opening. This chart aligns with a UK jeweller table. GIA publishes different millimetres for some letters, including K and O. That is a difference between tables, not a rounding slip.

No. The conversion chart is published on this page, with a row for each size and on-page anchors. We do not offer a downloadable PDF.

This page is the conversion chart. Our ring sizing guide explains how to measure, how we confirm a size, and how a resize works after delivery. The two pages use the same rows and link both ways.

EU size is the inner circumference in millimetres, rounded to the nearest whole number, which is the usual way ISO 8653 designation is shown.

No. Full eternity rings and some pavé settings cannot be resized without affecting the stones. Where the design allows it, we include one free resize within 1 month of delivery, through a local jeweller, with evidence. Full terms are on our aftercare and warranty page.

The ring must be round. Measure the inner diameter in millimetres, then find that diameter on this chart. Do not force the ring onto a stick. Our ring sizing guide has the fuller method.

Not sure which row applies to your measurement?

Ask us
Confirm your size

Send the millimetres, and we will sense check them

Include the chart or gauge you used and the intended band width. We confirm size before a ring is made.
Ask about a measurement Ring sizing guide