Ring Size Guide: Measure, Convert, Choose

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Why ring sizing causes so many problems

A sweater is easy to exchange, a ring much less so. If it is too small, it squeezes and leaves a mark; if it is too large, it spins around the finger or ends up falling off. Rings bought online are almost always returned because of an approximate measurement or a mix-up between two sizing systems.

The good news: in France, the system is simple. A ring's size corresponds to the inner circumference in millimeters. Measuring the circumference of your finger is therefore all you need to know your size. This page gives you the methods, the calculated conversion tables and the pitfalls to avoid. For choosing the stone and the setting, see also our page on gemstone rings.

The three measuring methods

1. The paper strip or thread. Cut a strip of thin paper about 10 cm by 5 mm, or take a non-stretch thread. Wrap it around the base of the finger, without squeezing and without any slack. Mark with a pen where the end meets the strip, unroll it flat along a rigid ruler and read the length in millimeters. That is your finger's circumference.

2. A ring that already fits. Lay it flat and measure its inner diameter, from one inner edge to the other through the centre. Multiply by 3.14 to get the circumference. A diameter of 17 mm gives about 53.4 mm. This method is reliable if the ring has a thin band; it is less so with a thick or domed band, whose inside may be narrower at some points.

3. The ring sizer. This is a set of reference rings, available from jewellers and sold inexpensively. Try several sizes on the finger concerned and keep the one that passes the knuckle with slight resistance and then turns without effort. It is the safest method, especially if your knuckles are pronounced.

Whichever method you use, measure two or three times, at different times of the day, and keep the most frequent value.

Conversion table

The diameter is calculated by dividing the circumference by pi (3.14159). American sizes are calculated with the formula published for the North American scale (diameter = 0.8128 × size + 11.63 mm) and rounded to the nearest quarter size; the Swiss size is the circumference minus 40. These are approximate equivalences: from one brand to another, a ring may differ by half a size.

French size (circumference in mm)	Inner diameter	Swiss size	US size (approx.)
46	14.6 mm	6	3 3/4
48	15.3 mm	8	4 1/2
50	15.9 mm	10	5 1/4
52	16.6 mm	12	6
54	17.2 mm	14	6 3/4
56	17.8 mm	16	7 3/4
58	18.5 mm	18	8 1/2
60	19.1 mm	20	9 1/4
62	19.7 mm	22	10
64	20.4 mm	24	10 3/4

British sizes, marked with letters, increase in steps of 1.25 mm of circumference: for these, use a jeweller's conversion chart or a ring sizer rather than an approximate calculation.

Pitfalls: what makes the size of your finger vary

• Time of day and temperature. Fingers are thinner in the morning and in cold weather, and wider at the end of the day and in strong heat. Measure at the end of the day, in a room at normal temperature, never right after a hot bath or coming in from the cold.
• The knuckle. If the knuckle is wider than the base of the finger, the ring must pass over the knuckle but must not spin once in place. Take the intermediate size, or measure both and average the results.
• Band width. A wide band (more than 6 mm) covers more skin and feels tighter than a thin band of the same size. It is often advised to take half a size to one full size up.
• The finger concerned. The thumb, index and ring fingers are not the same size, and the dominant hand is often slightly larger. Measure the exact finger that will wear the ring.
• Changes over time. Heat, salt, sport, fatigue, weight changes, pregnancy or certain health conditions can make fingers swell. If your size changes noticeably or your fingers swell for no clear reason, speak to a doctor.

If a ring becomes painful or the finger changes colour, remove the ring without delay. If it no longer fits, do not force it; consult a health professional or a jeweller. If a finger is very swollen or purplish, call 15 (the emergency number in France) or 112 (the emergency number across the European Union).

Example: finding your size step by step

1. You wrap a thread around your ring finger at the end of the day and read 54.5 mm.
2. You measure again the next morning: 53 mm. The finger therefore varies by 1.5 mm between these two moments.
3. You choose a thin ring: size 54 is suitable, because it passes the knuckle without spinning.
4. For an 8 mm wide band, you go up to size 55 or 56.
5. You check the length given on the product listing: some sellers state the inner size, others the diameter. A diameter of 17.2 mm does indeed correspond to size 54.

Adjustable rings, open rings and gifts

Adjustable rings (a band open at the back) tighten or loosen a little with the fingers. They are practical as a gift or for a finger whose size varies. They tolerate repeated opening and closing poorly: the metal can eventually break, especially if it is thin. Rings with a set stone and an open band withstand knocks less well than closed rings.

To give a ring without knowing the size, there are three options: choose an adjustable model, discreetly borrow a ring the person already wears on the same finger (and measure it on paper), or include an exchange voucher. The simplest is often to give another piece of jewellery, for example a pendant. See also our advice on giving a gemstone.

When to have a ring enlarged or reduced

A jeweller can enlarge or reduce a silver or gold ring by a few sizes, by adding or removing metal. The operation is more delicate if the ring has fragile stones or a decoration all around the band, or if it is made of steel or plated metal: heat can damage certain stones and the plating. Always ask for advice first. For the metals used in settings, read our page on the metals used in jewellery.

Frequently asked questions

Also read

The meanings mentioned belong to tradition and symbolism. They are neither promises of results nor medical advice. Back to Buying guides and gift ideas.