Ring Size Calculator

Measurement

Unit

Finger Circumference

Wrap a string around your finger, mark where it overlaps, then measure the string length. Enter the measurement above to find your ring size.

Your Ring Size

US 7

17.3 mm diameter | 54.4 mm circumference

Exact standard size match.

All Size Systems

Your ring size in 5 international standards

Physical Dimensions

Inner diameter and circumference of the ring

Diameter

17.3 mm

0.68"

Circumference

54.4 mm

2.14"

Ring Size Conversion Chart

Full US 0–13 international ring size reference

US	UK	EU	IN	JP	Dia	Circ
0	A	37	1	1	11.6	36.5
0.5	A	38	1	1	12	37.8
1	B	39	2	1	12.4	39.1
1.5	C	40	3	1	12.8	40.3
2	D	42	4	2	13.2	41.6
2.5	E	43	5	3	13.7	42.9
3	F	44	6	4	14.1	44.2
3.5	G	45	7	5	14.5	45.4
4	H	47	8	6	14.9	46.7
4.5	I	48	9	8	15.3	48

Ring sizes are approximate and may vary slightly between jewelers. Diameter and circumference are in millimeters. Always try on rings when possible for the best fit.

How Ring Size Conversion Works

Understanding the relationship between circumference and ring size standards

Ring sizing varies across countries because each system was developed independently. The key to accurate conversion is inner circumference in millimeters — the one universal measurement that all systems ultimately reference.

Circumference

Universal base measurement

Systems

International standards

Dia to Circ

Circumference = Diameter x pi

How the Calculator Works

This calculator converts between ring sizes by mapping each system to inner circumference in millimeters. Your input (measurement or known size) is first converted to circumference, then matched to the nearest standard size in each system. Since each system covers a different range, extreme measurements may fall outside some standards.

US sizes use the Jewelers of America mandrel standard (2.55mm per full size). UK uses letter-based British Standard sizing (1.25mm per letter). EU sizes equal inner circumference in mm (rounded).

Example — 54.4 mm Circumference (17.3 mm Diameter)

International Ring Size Systems

How ring sizing works in different regions around the world

US / Canada

Numeric sizes with half-size increments (3, 3.5, 4, ...). Based on the Jewelers of America mandrel. The most widely used system in North America.

Mandrel gauge | 2.55mm per size

UK / Australia / NZ

Letter-based system from A to Z, then Z+1, Z+2, etc. Based on the British Standard (BS 6820) mandrel. Also used in South Africa.

Letter gauge | 1.25mm per letter

EU (Continental Europe)

Ring size equals the inner circumference in millimeters, rounded to the nearest integer. An EU 54 ring has a 54mm inner circumference. Used across most of Europe.

ISO 8653 | Size = circumference mm

Indian

Numbered system used by Indian jewelers (Tanishq, CaratLane, etc.). Maps to the UK letter positions: Indian 1 = UK A, Indian 14 = UK N, etc.

Numeric | Maps to UK letters

Japanese (JIS)

Numbered system defined by JIS S 3040. Sizes 1 through 28, with approximately 1.05mm circumference per size. Starting at 41mm for size 1.

JIS S 3040 | 1.05mm per size

How to Measure Your Ring Size at Home

Two reliable methods using items you already have

Method 1: String or Paper Strip

1. Gather Materials

Get a thin strip of paper (about 1cm wide, 10cm long) or a piece of non-stretchy string, a pen, and a ruler with millimeter markings.

2. Wrap Around Finger

Wrap the paper or string snugly around the base of the finger you want to size. It should be snug but not tight — make sure it slides over your knuckle.

3. Mark the Overlap

Where the paper or string meets and overlaps, mark the exact point with a pen. This is your finger circumference.

4. Measure in mm

Lay the paper flat and measure from the end to your mark in millimeters. Enter this number as your circumference in the calculator above.

Method 2: Existing Ring

If you have a ring that fits well, place it on a ruler and measure the inner diameter (the widest point across the inside of the ring) in millimeters. Switch the calculator to "Diameter" mode and enter this measurement.

Measure in the evening when fingers are slightly larger. Avoid measuring when your hands are cold (fingers shrink) or after exercise (fingers swell). For the most accurate result, measure 2–3 times and use the average.

Common Ring Sizing Mistakes

Avoid these pitfalls when measuring or converting ring sizes

Measuring too tight or too loose

The string or paper should be snug but slide over the knuckle. Too tight gives a small size; too loose means the ring will slip off.

Ignoring the knuckle

Your knuckle is often wider than the base of your finger. The ring must fit over the knuckle, so size for the knuckle, not just the base.

Measuring at the wrong time

Fingers change size throughout the day and with temperature. Measure in the evening at room temperature for the most representative size.

Assuming all systems are equivalent

A "size 7" in the US system is NOT the same as size 7 in the Indian or Japanese system. Always specify which sizing standard you mean.

Using stretchy material to measure

Elastic string or stretchy tape will give an inaccurate (too small) reading. Use non-stretchy string, paper strip, or a proper ring sizer.

About the Ring Size Calculator

How this calculator works and what it covers

This calculator converts ring sizes across 5 international sizing systems (US, UK, EU, Indian, Japanese) using inner circumference as the universal reference. You can input a measurement (circumference or diameter in mm or inches) or convert from a known size in any system. Each system covers a specific range, so extreme measurements may fall outside some standards. All conversions are based on the Jewelers of America mandrel standard, British Standard BS 6820, ISO 8653, and JIS S 3040.

Frequently Asked Questions

Common questions about ring sizes and measurement