Ring sizing: the millimeter table

A ring should fit the finger it was made for.

How do I find my Alva ring size?
Measure the interior diameter of a ring that fits the intended finger, or measure the finger's circumference in millimeters. Match the measurement to Alva's chart below.

The number indicated on a ring’s sizing chart is just a code. More informative are the measurements listed below it – in millimeters. The first indicates the inner diameter, the second – the circumference of the ring.

Alva uses millimeters as its primary measure of ring sizes. Below are the equivalents in the US/Canada sizes;

US / Canada	Interior diameter	Interior circumference
3	14.1 mm	44.2 mm
3.5	14.5 mm	45.5 mm
4	14.9 mm	46.7 mm
4.5	15.3 mm	48.0 mm
5	15.7 mm	49.3 mm
5.5	16.1 mm	50.6 mm
6	16.5 mm	51.8 mm
6.5	16.9 mm	53.1 mm
7	17.3 mm	54.4 mm
7.5	17.7 mm	55.7 mm
8	18.1 mm	56.9 mm
8.5	18.5 mm	58.2 mm
9	18.9 mm	59.5 mm
9.5	19.4 mm	60.8 mm
10	19.8 mm	62.1 mm
10.5	20.2 mm	63.3 mm
11	20.6 mm	64.6 mm
11.5	21.0 mm	65.9 mm
12	21.4 mm	67.2 mm
12.5	21.8 mm	68.4 mm
13	22.2 mm	69.7 mm

Diameter and circumference

They describe the same interior space in two different ways.

Interior diameter is the distance across the ring (from one inner edge to the opposite inner edge).

Interior circumference is the distance around the ring.

If you have a ring that fits the intended finger well, diameter is the measurement you want. If you are measuring the finger, circumference is the measurement you need.

The difference seems small.

It is not.

A measurement made on the outside of a ring includes the metal in the measurement. It is not a useful indicator of the size of the hole through which the finger will pass.

Measuring a ring you already own

This is generally the simplest option, provided you have a ring that fits the intended finger well.

Use a ring that fits the intended finger well.

Place it on a flat surface and measure the distance across the ring (from one inner edge to the opposite inner edge) through the center. Do not measure the ring on its outside edge or include the width of the band in the measurement. Record the measurement in millimeters and compare it to the interior-diameter column above.

The ring you choose to measure should fit the intended finger well. A ring that is already too large or too small is not a useful reference.

Measuring the finger

If you do not have a ring that fits the intended finger, you can measure the finger itself.

You will need a strip of narrow paper that will not stretch.

Wrap the strip of paper around the base of the intended finger. The strip should be loose enough to be comfortable, but not so loose that it will not stay around the finger. Make a mark on the strip of paper where the tail meets the main part of the strip. Place the strip on a flat surface and measure the distance from the edge to the mark in millimeters. Compare this measurement to the circumference column in the Alva chart.

It is a good idea to take more than one measurement if you are measuring the finger. A millimeter difference can make a significant difference in fit.

The finger is not a rigid measuring device

A hand can change size throughout the day. Being particularly warm or cold can cause the fingers to swell or constrict. The measurement you take should indicate how the ring will fit most of the time. It should not be taken when the hands are particularly cold, for instance, and then compared to a standardized measurement that does not account for temperature.

The point is not to make the ring as tight as possible. The point is to make sure that it will pass over the knuckles and then settle comfortably against the finger.

The knuckles can be a particular challenge.

If the knuckles are substantially larger than the base of the finger, the ring must be able to pass over them to fit comfortably. It is a good idea to make sure that the measurement you have taken accounts for this.

When the two measurements conflict

Do not try to shoehorn a measurement to fit a desired size.

Take the measurement again.

Make sure the ring you used to measure fits the intended finger.

Make sure you measured the diameter of the ring correctly (from one inner edge to the opposite inner edge).

Make sure you measured the finger snugly enough that the paper would fit comfortably around the finger.

If the two measurements continue to disagree, professional sizing is the best option, particularly for a ring that is particularly wide, substantial, difficult to resize, or custom made.

A millimeter is a small unit of measurement.

It is also an extremely important one.

The width of the band can make a significant difference to how a ring feels when it is worn.

Two rings of the same size can feel substantially different if one has a very narrow band and the other has a broad, heavy band.

This is one reason it is important to think of a ring size as a measurement rather than a universal standard. The number on the ring is less important than the object the number is describing.

The ring size is a characteristic of the ring. The fit is a characteristic of the finger.

For an important purchase, the ring should be considered in both ways.

International sizing

There is no international standard for ring sizes. The same ring can have different numbers or letters depending on the country of sale.

Alva's supplied chart includes the following systems:

US / Canada

British / Irish

Japanese

Swiss

Australian

The underlying millimeter measurements are the standard that the other measurements are based on.

When comparing international measurements, it is a good idea to use millimeters as a reference rather than assuming that a size "7" in one system is the same as a size "7" in another.

The measurement is more important than the label

Ring sizes are useful in that they allow customers to purchase rings without measuring. Millimeters are useful in that they describe the object being measured.

A US 7 is a label.

17.3 mm is a measurement.

For Alva, the measurement is more important than the label. The chart exists to allow the measurement to be understood.

When in doubt, do not guess at a ring size based on someone else's ring. Measure the finger, measure a ring that fits, and compare the two using the chart.

A ring is a small object.

Its fit should not be approximated.