UK & Australian ring size chart

Every letter on the British scale, A to Z+6, with every half letter — its inner circumference and diameter in millimetres, and the nearest US and EU size. Ireland, Australia and New Zealand use the same letters.

A letter is a length. Size A is 37.50 mm around the inside, and every letter adds 1.25 mm. So when a shop’s letter and a chart disagree, the millimetres settle it — and in Australia, as it turns out, they disagree a lot.

Don’t know your size yet? The ring sizer measures it against your screen and gives the letter beside the millimetres. No screen to hand? Print a paper ring sizer instead.

Every letter, A to Z+6

Find your letter and read across for the US size. Circumference is what a paper strip round your finger measures; diameter is what you measure straight across a ring you already own.

UK, Irish, Australian and New Zealand ring sizes from A to Z+6 in half letters, with inner circumference and diameter in millimetres, US/Canada size and EU/ISO size.
UK / IE / AU / NZ	Circumference	Diameter	US / CA	EU / ISO
A	37.50 mm	11.94 mm	0¼	—
A½	38.13 mm	12.14 mm	0½	—
B	38.75 mm	12.33 mm	0¾	—
B½	39.38 mm	12.53 mm	1	—
C	40.00 mm	12.73 mm	1¼	—
C½	40.63 mm	12.93 mm	1½	41
D	41.25 mm	13.13 mm	1¾	41
D½	41.88 mm	13.33 mm	2	42
E	42.50 mm	13.53 mm	2¼	43
E½	43.13 mm	13.73 mm	2½	43
F	43.75 mm	13.93 mm	2¾	44
F½	44.38 mm	14.13 mm	3	44
G	45.00 mm	14.32 mm	3¼	45
G½	45.63 mm	14.52 mm	3½	46
H	46.25 mm	14.72 mm	3¾	46
H½	46.88 mm	14.92 mm	4	47
I	47.50 mm	15.12 mm	4¼	48
I½	48.13 mm	15.32 mm	4½	48
J	48.75 mm	15.52 mm	4¾	49
J½	49.38 mm	15.72 mm	5	49
K	50.00 mm	15.92 mm	5¼	50
K½	50.63 mm	16.11 mm	5½	51
L	51.25 mm	16.31 mm	5¾	51
L½	51.88 mm	16.51 mm	6	52
M	52.50 mm	16.71 mm	6¼	52
M½	53.13 mm	16.91 mm	6½	53
N	53.75 mm	17.11 mm	6¾	54
N½	54.38 mm	17.31 mm	7	54
O	55.00 mm	17.51 mm	7¼	55
O½	55.63 mm	17.71 mm	7½	56
P	56.25 mm	17.90 mm	7¾	56
P½	56.88 mm	18.10 mm	8	57
Q	57.50 mm	18.30 mm	8¼	58
Q½	58.13 mm	18.50 mm	8½	58
R	58.75 mm	18.70 mm	8¾	59
R½	59.37 mm	18.90 mm	9	59
S	60.00 mm	19.10 mm	9¼	60
S½	60.63 mm	19.30 mm	9½	61
T	61.25 mm	19.50 mm	9¾	61
T½	61.88 mm	19.70 mm	10	62
U	62.50 mm	19.89 mm	10¼	63
U½	63.13 mm	20.09 mm	10½	63
V	63.75 mm	20.29 mm	10¾	64
V½	64.38 mm	20.49 mm	11	64
W	65.00 mm	20.69 mm	11¼	65
W½	65.63 mm	20.89 mm	11½	66
X	66.25 mm	21.09 mm	11¾	66
X½	66.88 mm	21.29 mm	12	67
Y	67.50 mm	21.49 mm	12	68
Y½	68.13 mm	21.68 mm	12¼	68
Z	68.75 mm	21.88 mm	12½	69
Z½	69.38 mm	22.08 mm	12¾	69
Z+1	70.00 mm	22.28 mm	13	70
Z+1½	70.63 mm	22.48 mm	13¼	71
Z+2	71.25 mm	22.68 mm	13½	71
Z+2½	71.88 mm	22.88 mm	13¾	72
Z+3	72.50 mm	23.08 mm	14	73
Z+3½	73.13 mm	23.28 mm	14¼	73
Z+4	73.75 mm	23.48 mm	14½	74
Z+4½	74.38 mm	23.67 mm	14¾	74
Z+5	75.00 mm	23.87 mm	15	75
Z+5½	75.63 mm	24.07 mm	15¼	76
Z+6	76.25 mm	24.27 mm	15½	76

US sizes are to the nearest quarter, the smallest step US jewellers sell. X½ and Y both come out as US 12: a half letter is 0.625 mm around and a US quarter 0.638 mm, so the two scales slowly drift and now and then two letters share a quarter. Below C½ there is no EU/ISO size, because ISO 8653 does not define one. Every other system, in quarter US sizes, is on the full ring size chart.

US to UK ring size

Find your US size and read across. The third column is for a shop that stocks whole letters only, as many do. If your size is a half letter there, buy the letter above, not the one below. Between two sizes, bigger is the safer mistake: the smaller ring is tighter than the finger you measured and may not pass the knuckle, while the bigger one is a fraction loose.

US ring sizes 3 to 13 converted to UK and Australian letters, with the whole letter to buy and the inner circumference in millimetres.
US / CA	UK / AU	Whole letters only? Buy	Circumference
3	F½	G	44.21 mm
3½	G½	H	45.48 mm
4	H½	I	46.76 mm
4½	I½	J	48.04 mm
5	J½	K	49.31 mm
5½	K½	L	50.59 mm
6	L½	M	51.87 mm
6½	M½	N	53.14 mm
7	N½	O	54.42 mm
7½	O½	P	55.70 mm
8	P½	Q	56.97 mm
8½	Q½	R	58.25 mm
9	R½	S	59.53 mm
9½	S½	T	60.80 mm
10	T½	U	62.08 mm
10½	U½	V	63.36 mm
11	V½	W	64.64 mm
11½	W½	X	65.91 mm
12	Y	Y	67.19 mm
12½	Z	Z	68.47 mm
13	Z+1	Z+1	69.74 mm

Why a US 6 comes out as L½ here but M on many charts is worked through, step by step, on the ring sizer page.

How the letter scale works

Size A is a ring 37.50 mm around the inside. Each letter after it adds 1.25 mm, and a half letter adds 0.625 mm. That is the rule the British Standards Institution adopted when it metricated the scale in 1987, and it is the whole scale — there is no table to memorise.

Working out a letter yourself

Take the circumference in millimetres. A paper strip reading 57 mm, say.
Subtract 37.5 and divide by 1.25: (57 − 37.5) ÷ 1.25 = 15.6.
Round to the nearest half: 15.5.
Count the letters from A as 0. Number 15 is P, so 15.5 is P½.

Measured straight across a ring instead? Multiply the diameter by π (3.1416) first.

After Z the alphabet runs out, so the scale keeps counting: Z+1, Z+2 and on to Z+6, each still 1.25 mm apart. Some charts write them Z1, Z2. The British scale names nothing past Z+6, and neither does this page.

Source: the 1987 rule is attributed to BS 6820:1987, the British adoption of ISO 8653. The standard is paywalled and we have not read it, so we claim no more than the rule itself, which Wikipedia states as C = 40 mm and 1.25 mm per letter.

What UK jewellers actually use

We read the size guides of six UK high-street chains on 26 September 2026. Four of them put L at 51.2 mm and M at 52.5 mm around — this chart to within 0.05 mm. The other two, which belong to one group, run half a letter higher from H to R: their M is 51.87 mm, which is L½ here.

So in Britain a letter means close to the same ring from shop to shop — never more than half a letter out. To move a size from one shop to another, carry the millimetres, not the letter.

Australia and New Zealand: same letters, looser charts

Australia, New Zealand and Ireland size rings with the same letters as Britain, so the chart above works for all of them. In Australia, though, what a letter means moves around far more from shop to shop.

Inner circumference of sizes L and M on this chart, on most UK high-street charts, and on three Australian jewellers’ published charts.
Chart	L, around	M, around
This page (the 1.25 mm rule)	51.25 mm	52.50 mm
UK high street (4 of 6 chains)	51.2 mm	52.5 mm
Australian jeweller 1	50.58 mm	51.87 mm
Australian jeweller 2(from its diameters)	51.55 mm	52.81 mm
Australian jeweller 3	51.9 mm	53.2 mm

Read from three Australian jewellers’ own size guides on 2 October 2026. An Australian M runs from 51.87 mm to 53.2 mm depending on the shop: 1.33 mm apart, more than a whole letter. One of the three quotes the 1.25 mm rule in its own guide, and its chart sits about 0.3 mm above it.

So in Australia, don’t carry a letter from one shop to another. Get your size in millimetres — measure it, or ask a jeweller to — and look that figure up on the chart of the shop you are buying from. For a US size, use the US column above, then check it against that shop’s millimetres.

We have not compared New Zealand or Irish jewellers’ charts closely enough to say how well they agree, so this page makes no claim either way.

UK ring size questions

Word for word, the questions Google shows US searchers for “uk ring size chart”. Nothing here is invented to pad the page.

How do I find my UK ring size?

Get the size in millimetres, then turn it into a letter. Measure straight across the inside of a ring that fits and multiply by π, or wrap a paper strip round the base of the finger and measure it flat; either way you have the inner circumference. Subtract 37.5 and divide by 1.25, then round to the nearest half. Counting A as 0, 11 is L and 11.5 is L½. If the jeweller stocks whole letters only, take the letter above a half. The ring sizer on this site does the arithmetic for you and shows the letter beside the millimetres.

What is a 21 mm ring size in US size?

US 11½, if 21 mm is the inside diameter, the distance straight across the ring. That is UK X and 65.97 mm around. If you meant 21 mm round the finger, measure again: that is smaller than any adult ring, and the smallest UK letter, A, is 37.50 mm around.

How much bigger is a size 8 ring than a 7?

One US size is 0.81 mm of inside diameter, which is 2.55 mm around. In UK letters, US 7 is N½ and US 8 is P½, two whole letters apart. US 7½ sits between them at UK O½, and US jewellers also sell quarter sizes, each 0.64 mm around.