How do I measure my ring size?

The most accurate way is to visit a jeweler. For home measurement, wrap a string around your finger, mark where it overlaps, and measure the length in millimeters. This is your circumference.

What is the difference between diameter and circumference?

Diameter is the width across the inside of the ring, while circumference is the distance around the inside. Circumference = Diameter × π (3.14159).

Do ring sizes vary between countries?

Yes, each country has its own sizing system. US sizes are numeric (e.g., 7), UK uses letters (e.g., N), while EU and JP use millimeters.

Convert UK Ring Size W to mm

Easily convert UK ring size W to mm. This calculator gives you the exact millimeter measurements, ensuring a perfect fit.

Size Converter

Select your current size and system

Region

Size

Single letter A-Z

Converted Sizes

Converted Size

mm Standard

All Regional Sizes

mm (Circ)

Reference Table

Complete size conversion chart

US	UK	EU	JP	AU	CH	DE	mm	mm (Circ)
3	F	44	4	F	4	14	14.1	44.2
3.5	G	45	5	G	5.25	14.5	14.5	45.5
4	H	46.5	7	H	6.5	15	14.9	46.8
4.5	I	48	8	I	7.75	15.25	15.3	48
5	J 1/2	49	9	J 1/2	9	15.75	15.7	49.3
5.5	L	50.5	10	L	10.25	16	16.1	50.6
6	M	52	12	M	11.5	16.5	16.5	51.9
6.5	N	53	13	N	12.75	17	16.9	53.1
7	O	54.5	14	O	14	17.25	17.3	54.4
7.5	P	56	15	P	15.25	17.75	17.7	55.7
8	Q	57	16	Q	16.5	18	18.1	57
8.5	R	58.5	17	R	17.75	18.5	18.5	58.3
9	S	59.5	18	S	19	19	19	59.5
9.5	T	61	19	T	20.25	19.5	19.4	60.8
10	U	62	20	U	21.5	20	19.8	62.1
10.5	V	63.5	22	V	22.75	20.25	20.2	63.4
11	W	65	23	W	24	20.75	20.6	64.6
11.5	X	66	24	X	25.25	21	21	65.9
12	Y	67.5	25	Y	26.5	21.25	21.4	67.2
12.5	Z	69	26	Z	27.75	21.75	21.8	68.5
13	Z+1	70	27	Z+1	29	22.25	22.2	69.7

Frequently Asked Questions

📏 How to Measure Your Ring Size

Method 1: String or Paper

The most common way to measure at home. Follow these steps carefully:

Step-by-step guide showing how to measure ring size using paper or string method: wrap around finger, mark overlap, measure length in millimeters

Wrap a strip of paper or string around the base of your finger.
Mark the point where the ends meet with a pen.
Measure the string or paper with a ruler (mm).

Method 2: Existing Ring

If you have a ring that fits well, use this method:

Diagram showing how to measure existing ring inner diameter with a ruler, measuring across the inside edge

Place your ring on a flat surface.
Place a ruler on top of the ring.
Measure the inner diameter (inside edge to inside edge).

💡 Pro Tip: Avoid Common Mistakes

Comparison showing incorrect (too tight) vs correct (snug fit) ring measurement technique with paper around finger

Don't pull the string too tight!

The paper or string should fit snugly around your finger, but not so tight that it squeezes your skin. It needs to be able to slide over your knuckle with just a little bit of resistance.

✓ Correct: Snug fit, comfortable
✗ Incorrect: Squeezing finger, too tight

🛡️ Our Methodology & Accuracy Standards

Data Verification: All ring size conversion data is cross-referenced against the ISO 8653:2016 jewelry sizing standard and official manufacturer charts from major international jewelry retailers.

Precision Calculation: Conversions between diameter and circumference use a high-precision constant for π (3.1415926535), ensuring that millimeter results are accurate to within 0.01mm.

Regional Authority: We distinguish between true EU sizing (circumference in mm) and the older DE/Central European standards. Our UK scaling adheres to the traditional British Standard 1283.

Continuous Updates: Our database is reviewed regularly for changes in international manufacturing tolerances to provide reliable, up-to-date guidance for jewelry shopping.

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Understanding your UK W conversion

A UK ring size W is a standard measurement used in jewelry manufacturing across the United Kingdom and Australia. Converting this to mm requires precise mathematical scaling to ensure the ring sits comfortably on your finger.

Finger Swelling Factors

Did you know your finger can change by a half size depending on the time of day? We recommend measuring in the evening when your fingers are at their largest to avoid a ring that's too tight.

Accuracy Guarantee

Our conversion logic is based on the ISO 8653:2016 international standard. This ensures that UK W is mapped precisely to its global equivalent in millimeters and regional scales.

Common Conversion Tips

Wide Bands: If the ring you are buying has a band wider than 6mm, consider going up half a size from your measured UK W.
Comfort Fit: Comfort fit rings have a rounded inside. You may need to go down a half size if you are switching from a standard fit to a comfort fit.
Knuckle Size: If your knuckle is significantly larger than the base of your finger, measure both and choose a size in between.