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Category Utilities

Select Region & Size

⚠ Uncalibrated. Use a card to calibrate for accuracy.

Diameter 16.51 mm

US Size 6

Adjust Ring Size

Fine Tune

1. Wrap a thin strip of paper or string around the base of the finger.

2. Mark the point where the ends meet.

3. Measure the length with a ruler (mm).

Measured Length (Circumference)

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About

Accurate ring sizing is critical for purchasing jewelry, yet the lack of a unified global standard often leads to costly errors and returns. The difference between sizes can be as small as 0.4 mm in diameter, meaning even minor measurement inaccuracies result in an ill-fitting ring.

This tool solves the standardization problem by cross-referencing over 60 distinct size definitions across 7 major regional standards. Unlike simple lookup tables, this utility includes a calibrated Virtual Sizer that utilizes your device's screen pixel density to measure existing rings, and a Wrap Calculator for converting finger circumference (C) to diameter (d) using the fundamental relation d = C ÷ π.

Formulas

The core mathematical relationship between ring diameter and circumference is governed by the circle constant π.

{

d = Cπ for diameter from circumferenceC = d × π for circumference from diameter

When calibrating the screen for the Virtual Sizer, we calculate a Pixel-to-Millimeter density ratio (R_px) based on a known reference object width (e.g., Credit Card width ≈ 85.60 mm):

R_px = Width_px85.60

This ratio allows us to render a virtual circle of exact physical diameter (d_ring) on the DOM:

ElementWidth_px = d_ring × R_px

Reference Data

Diameter (mm)	US / Canada	UK / Aus	EU / ISO	Japan	Swiss	Brazil
14.07	3	F	44	4	4	10
14.27	3 ¼	F ½	44.5	4.5	4.75	10.5
14.48	3 ½	G	45.5	5	5.25	11
14.68	3 ¾	G ½	46	5.5	6	11.5
14.88	4	H	47	6	6.5	12
15.09	4 ¼	H ½	47.5	6.5	7	13
15.29	4 ½	I	48.5	7	7.75	13.5
15.49	4 ¾	J	49	8	8.5	14.5
15.70	5	J ½	50	9	9	15
15.90	5 ¼	K	50.5	9.5	10	16
16.10	5 ½	K ½	51.5	10	10.5	17
16.31	5 ¾	L	52	10.5	11.25	17.5
16.51	6	L ½	53	11	11.75	18
16.71	6 ¼	M	53.5	11.5	12.5	19
16.92	6 ½	M ½	54.5	12	13.25	20
17.12	6 ¾	N	55	12.5	14	20.5
17.32	7	N ½	56	13	14.5	21
17.53	7 ¼	O	56.5	13.5	15.25	22
17.73	7 ½	O ½	57.5	14	16	23
17.93	7 ¾	P	58	15	16.5	24
18.14	8	P ½	59	16	17.25	25
18.34	8 ¼	Q	59.5	16.5	18	26
18.54	8 ½	Q ½	60.5	17	19	27
18.75	8 ¾	R	61	17.5	19.5	28
18.95	9	R ½	62	18	20.25	29
19.15	9 ¼	S	62.5	18.5	21	30
19.35	9 ½	S ½	63.5	19	21.5	31
19.56	9 ¾	T	64	19.5	22.25	32
19.76	10	T ½	65	20	23	33
19.96	10 ¼	U	66	21	23.5	33.5
20.17	10 ½	U ½	67	21.5	24.25	34
20.37	10 ¾	V	67.5	22	25	35
20.57	11	V ½	68.5	23	26	36
20.78	11 ¼	W	69	23.5	26.5	37
20.98	11 ½	W ½	70	24	27.25	38
21.18	11 ¾	X	71	24.5	28	39
21.39	12	X ½	72	25	28.5	40
21.59	12 ¼	Y	72.5	26	29.25	41
21.79	12 ½	Y ½	73.5	26.5	30	42
22.00	12 ¾	Z	74	27	31	43
22.20	13	Z+1	75	27.5	31.75	44

Frequently Asked Questions

Accuracy depends entirely on calibration. Without calibration, the tool guesses your screen density (DPI), which varies wildly between devices (e.g., iPhone vs. Desktop). By using the "Calibrate" feature with a standard credit card, you establish a precise pixel-to-millimeter ratio, achieving accuracy within 0.5mm.

Measuring an existing ring that fits well is generally more accurate. Finger tissue is soft and compressible, leading to errors if the string/tape is pulled too tight or too loose. If measuring the finger, measure the knuckle as well to ensure the ring can slide over it.

Always size up. Fingers swell due to heat, salt intake, and time of day. A slightly larger ring is wearable; a ring that is too small may cut off circulation or be impossible to remove.

Both Australia and the UK use the British wheatsheaf letter system (A-Z). This system is also commonly used in Ireland, New Zealand, and South Africa.

Screen Calibration

About

Formulas

Reference Data

Frequently Asked Questions