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Ring Size Calculator

Find your ring size in USA/Canada, UK/Australia, EU/ISO, Germany, Japan, and India sizing. Enter the inside diameter or circumference to get your size across all major international systems.

Units

Measure the straight distance across the inside of the ring from inner edge to inner edge.

Measure the distance around the inside of the ring. Equals diameter × π.

Ring sizes are approximate

Different manufacturers and countries may vary slightly from these conversions. For best accuracy, have your finger measured by a professional jeweler using a ring sizer.

How to Measure Ring Size

Method 1 — Measure an Existing Ring

Take a ring that already fits the intended finger well. Measure the inside diameter — the straight distance across the inner circle from one inside edge to the other. A ruler or digital calipers works best.

Two rings: the first shows inside diameter measured as a straight line across the center, the second shows inside circumference measured around the inner edge

Enter this measurement into the calculator above as the Inside Diameter. The calculator automatically computes the circumference and shows your size in all major international systems.

Method 2 — Measure Your Finger

Three-step guide: Step 1 — wrap a paper strip around the finger, Step 2 — mark where the ends overlap, Step 3 — measure the length with a ruler
  1. Wrap a thin strip of paper or a flexible measuring tape around the base of your finger. It should be snug but not tight — you should be able to slide it over your knuckle with slight resistance.
  2. Mark the point where the strip overlaps. A fine pen works better than pencil for a precise mark.
  3. Measure the length from the end of the strip to the mark in millimetres. This is your inside circumference.

Tips for accurate measurement: Measure at the end of the day when your hands are warm. Avoid string or elastic — they stretch. A narrow strip of printer paper (about 5 mm wide) works best. Measure 2–3 times and average the results.

Ring Size Conversion Charts

USA / Canada Ring Sizes

Inside Diameter (mm)Inside Circumference (mm)US / CA Size
14.144.23
14.545.53½
14.946.84
15.348.04½
15.749.35
16.150.65½
16.551.96
16.953.16½
17.354.47
17.755.77½
18.157.08
18.558.28½
19.059.69
19.460.99½
19.862.210
20.263.510½
20.664.811
21.066.011½
21.467.312
21.868.512½
22.269.813

Each full US size increases the inside diameter by 0.8128 mm (or circumference by 2.55 mm). Quarter sizes (¼, ½, ¾) are standard in jewelry stores.

UK / Australia Ring Sizes

Inside Circumference (mm)UK / AU SizeInside Circumference (mm)UK / AU Size
40.0C53.1M½
40.6C½53.8N
41.3D54.4N½
41.9D½55.0O
42.5E55.6O½
43.1E½56.3P
43.8F56.9P½
44.4F½57.5Q
45.0G58.1Q½
45.6G½58.8R
46.3H59.4R½
46.9H½60.0S
47.5I60.6S½
48.1I½61.3T
48.8J61.9T½
49.4J½62.5U
50.0K63.1U½
50.6K½63.8V
51.3L64.4V½
51.9L½65.0W
52.5M

Each half-letter step adds 0.625 mm to the inside circumference. UK size C equals 40.0 mm inside circumference.

International Ring Size Comparison

Diam (mm)US / CAUK / AUEU / ISOGermanyJapanIndia
14.94H½4715.077
15.34½I4815.587
15.75J½4915.598
16.15½K5116.0109
16.56L½5216.51110
16.96½M½5317.01211
17.37N½5417.51312
17.77½O½5617.51413
18.18P½5718.01514
18.58½Q½5818.51615
19.09S6019.01817
19.49½T6119.51918
19.810U6220.02019
20.210½V6320.02120
20.611W6520.52221
21.011½X½6621.02322
21.412Y6721.52423
21.812½Z6822.02524
22.213Z+17022.02726

These conversions follow ISO 8653:2016 and BS 6820:1987 standards. Slight variations (up to 0.5 mm) exist between manufacturers.

A note on sizing accuracy: Ring sizing standards vary slightly between countries and even between jewelers within the same country. The values in this calculator and charts are based on international standards. For the most accurate fit, always try on a ring in person or use a professional ring sizer. A ring that is slightly too large can be resized down by most jewelers; a ring that is too small is harder to adjust.

Frequently Asked Questions

How do I measure my ring size at home?

There are two reliable methods. **Method 1 — Measure an existing ring:** Take a ring that fits the intended finger and measure its inside diameter with a ruler (straight across from inner edge to inner edge). **Method 2 — Measure your finger:** Wrap a thin strip of paper around the base of your finger, mark where it overlaps, then measure the length with a ruler to get the inside circumference. The calculator accepts either measurement.

Which is more accurate — measuring a ring or my finger?

Measuring an existing ring that fits well is more reliable. Finger size changes throughout the day with temperature, activity, and diet. If measuring your finger, do it at the end of the day when your hands are warm. Cold fingers can be up to half a size smaller.

What's the difference between inside diameter and inside circumference?

The inside diameter is the straight-line distance across the inner circle from edge to edge. The inside circumference is the distance all the way around the inside of the ring. They are related by C = pi × D. Enter either value and the calculator automatically computes the other.

How does US/Canada ring sizing work?

The US and Canada use a numeric scale from about 3 to 16 in quarter-size increments (3, 3.25, 3.5, 3.75, …). Each full size increases the inside diameter by 0.8128 mm. Half sizes (e.g. 7.5) and quarter sizes (e.g. 7.25) are common. A women's average is around size 6–7; men's average is around 9–10.

How does UK/Australia ring sizing work?

The UK and Australia use letters: A, A½, B, B½, C, C½, … through Z and beyond (Z+1, Z+2, etc.). Each half-letter step corresponds to 0.625 mm of inside circumference. UK size C equals 40 mm inside circumference.

How does European (ISO) ring sizing work?

The international standard ISO 8653:2016 defines ring size as the inside circumference in millimetres. For example, EU/ISO size 54 means the ring has a 54 mm inside circumference. This is the most widely used system across Europe.

How does German ring sizing work?

German sizes use the inside diameter in millimetres, rounded to the nearest 0.5 mm. For example, an inside diameter of 17.3 mm equals German size 17.5.

How do Japanese and Indian ring sizes work?

Japan uses a numeric scale from 1 to 27, and India from 1 to about 30. Both are based on inside diameter ranges. For example, a diameter of 17.3 mm corresponds to Japanese size 13 and Indian size 12.