Jewellery tools / Sizing

Ring size converter

Compare a known size or inside measurement with the supported Australian/UK, US and European sizes in one reference chart.

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Choose a size or measurement to see the closest supported chart entry.

How this conversion works

European sizes in this chart equal finger circumference in whole millimetres. We show the Cartier chart’s US and UK equivalents. The approximate inside diameter is calculated as circumference ÷ π and rounded to one decimal place. Measurements between entries are matched to the nearest supported row; ties go to the larger size.

This is a conversion guide, not a guaranteed fit. Retailers use different charts, and band shape and width affect comfort. Confirm your retailer’s sizing and seek professional sizing before ordering.

Source: Cartier ring sizing table, checked 27 October 2026. Cartier’s chart is used consistently here; other retailer charts may differ.

Browse jewellers and check each listing’s recorded services →

Reference chart

European size and inside circumference are the same whole-millimetre value in the source. Inside diameter is approximate.

Supported Cartier ring-size conversions, EU 44 to 69
AU/UK	US	EU	Circumference	Diameter, approx.
F 1/2	3	44	44 mm	14.0 mm
G	3 1/4	45	45 mm	14.3 mm
H	3 3/4	46	46 mm	14.6 mm
H 1/2	4	47	47 mm	15.0 mm
I 1/2	4 1/2	48	48 mm	15.3 mm
J 1/2	4 3/4	49	49 mm	15.6 mm
K	5 1/4	50	50 mm	15.9 mm
L	5 3/4	51	51 mm	16.2 mm
L 1/2	6	52	52 mm	16.6 mm
M 1/2	6 1/4	53	53 mm	16.9 mm
N 1/2	6 3/4	54	54 mm	17.2 mm
O	7 1/4	55	55 mm	17.5 mm
P	7 1/2	56	56 mm	17.8 mm
P 1/2	8	57	57 mm	18.1 mm
Q 1/2	8 1/4	58	58 mm	18.5 mm
R	8 3/4	59	59 mm	18.8 mm
S	9	60	60 mm	19.1 mm
S 1/2	9 1/2	61	61 mm	19.4 mm
T 1/2	10	62	62 mm	19.7 mm
U 1/2	10 1/4	63	63 mm	20.1 mm
V	10 3/4	64	64 mm	20.4 mm
W	11	65	65 mm	20.7 mm
W 1/2	11 1/2	66	66 mm	21.0 mm
X 1/2	11 3/4	67	67 mm	21.3 mm
Z	12 1/4	68	68 mm	21.6 mm
Z 1/2	12 1/2	69	69 mm	22.0 mm