Ring size charts for the US, UK, Australia and Europe

What does a ring size chart measure?

Every chart describes one thing: the inside of the band, the edge that touches the finger. The inner diameter is the distance straight across that edge, and the inner circumference is the distance around it, always the diameter times π (about 3.14).

Metal thickness never changes the size, because every chart measures the inside of the shank. What changes from chart to chart is the unit, and whether it counts across the ring or around it. The glossary entry on ring size has the short version.

How does the US ring size scale work?

US sizes are a numbered scale on the inner diameter. Size 0 is 11.63 mm across, and each whole size adds 0.8128 mm, which is exactly 0.032 of an inch.

inner diameter (mm) = 11.63 + 0.8128 × US size

A US 6 is 11.63 + 6 × 0.8128, which comes to 16.5 mm across. Half sizes are a normal part of the scale: a US 6½ is 16.9 mm.

Around the finger, each whole US size adds about 2.55 mm of circumference, which is why US and EU numbers climb at such different rates.

How do UK and Australian letter sizes work?

UK sizes are letters. A is about a US ½, and each letter after it is about half a US size larger, so a US 6 lands on L and a US 6½ on M. Half letters, such as L½, sit about a quarter of a US size above the whole letter.

Australia and New Zealand use the same letters, so one column of a chart covers all three countries.

A given ring often measures between two letters, and charts round that in different directions, so two charts can give the same finger neighbouring letters.

How do EU sizes work?

The EU size, also called the ISO size, is the inner circumference in millimetres, with no scale on top. A ring that measures 52 mm around the inside is an EU 52.

That makes EU the one size you can read straight off a measurement: wrap a strip of paper around the finger, mark where it overlaps, and the length in millimetres is the EU size. A US 6, at 16.5 mm across, is 16.5 × π, or 51.9 mm, around: an EU 52 to the nearest millimetre.

How do you convert a ring size from one chart to another?

Go through the inner diameter. Reading across from one printed chart to another rounds the size twice, and the errors add up.

1. Turn your size into a diameter. For a US size, work out 11.63 plus 0.8128 times the size. For an EU size, divide by π. For a UK or Australian letter, count half sizes up from A, which is US ½, to find the US size: L, the twelfth letter, is a US 6. Then use the US formula.
2. Turn the diameter into the size you need. For US, subtract 11.63 and divide by 0.8128. For EU, multiply by π. For a UK letter, take the US result and count half sizes up from A.
3. Round once, at the end. Round US sizes to a half step, UK sizes to a letter or half letter, and EU sizes to a whole number of millimetres, and note which way you rounded.

A worked example: an EU 54 is 54 ÷ π, or 17.19 mm across, which works out at US 6.84. Rounded to the nearest half size that is a US 7; rounded down, a 6½. The nearest UK letter is N. Both US readings describe the same ring, so say which way you rounded when you pass a size on.

The ring size converter runs these steps for you and gives the size in US, UK and Australian, EU and millimetres.

Ring size chart: US, UK and Australia, EU

Whole US sizes, worked out from the formula above. Each half US size lands on the letter in between, so a US 5½ is a K and a US 7½ is an O.

The UK column gives the nearest letter, as the converter does; another chart may print the neighbouring letter or a half letter for the same ring. The converter also has the full chart in half sizes.

Why do two charts give different sizes?

Three things make charts disagree.

1. Rounding. A finger rarely measures exactly on a size, and a chart can round to the nearest step, up or down. Half a letter or half a size between two charts can be rounding alone.
2. Diameter or circumference. One chart's millimetre column can be another chart's EU size.
3. The band and the finger. A wide band sits tighter than a narrow one at the same size, and fingers change through the day. No chart accounts for either.

How do you get a size you can trust?

1. Measure what you have. Measure across the inside of a ring that already fits, or wrap paper around the finger. Measuring your ring size at home covers both methods.
2. Convert once. Put that one measurement through the converter.
3. Confirm it with a jeweller's gauge. A finger gauge is a set of sized rings you try on; a ring mandrel is a tapered, marked rod a jeweller slides a ring onto to read its size. Either settles what a chart only approximates.

Seeing the ring on a hand helps too. Virtual ring try-on shows the ring on your hand through the camera and, after a few seconds with your palm flat to it, estimates your size with its range, since a camera cannot measure exact size. If you know your size, you can enter it instead.

How the ring builder handles sizes

If you sell rings online, offer the systems your shoppers already know and convert behind the scenes. In the ring builder, the Ring size step offers US, UK and EU sizes, and try-on sizes the ring to the size the shopper picks. A UK letter or EU number is also converted to a US size and an inner diameter, so the workshop still gets a size it can cut. The builder, try-on and the converter read one size table, so a size means the same millimetres in each.