How to find your ring size without guessing

Q: How do you find your ring size?

In France, ring size equals the inner circumference in millimetres: a size 52 corresponds to a 52 mm finger circumference. Two methods work at home. Wrap the finger with a non-elastic string, mark the overlap point and measure the length with a ruler. Or measure the inner diameter of a ring that already fits and multiply it by 3.14.

Q: What time of day should you measure your finger?

Late in the day and at normal temperature. Fingers swell with heat, effort and water retention, and are thinner in the morning or in cold weather. A measurement taken on a winter morning easily gives half a size less than everyday reality.

Q: What if you are between two sizes?

Take the larger size in most cases. A slightly loose ring can be fixed with a size reducer or resized by a jeweller, whereas a ring that is too tight will not pass the knuckle. The exception is wide band rings, which feel tighter at the same size.

In short:
In France, ring size is the inner circumference in millimetres: size 52 means a 52 mm finger circumference.
Two home methods suffice: a non-elastic string measured with a ruler, or the diameter of an existing ring multiplied by 3.14.
Measure late in the day at normal temperature, since a finger measured on a winter morning easily gives half a size less.
When in doubt, the larger size can be corrected, the smaller one will not pass the knuckle.

What the number means

French ring size is directly the inner circumference in millimetres. A size 54 ring has a 54 mm inner circumference. This system is more readable than US sizes, which follow an arbitrary scale.

France / Europe	Inner diameter	US
48	15.3 mm	4.5
50	15.9 mm	5.25
52	16.6 mm	6
54	17.2 mm	6.75
56	17.8 mm	7.5
58	18.5 mm	8.25

The two home methods

The string method

Wrap the base of the finger with a non-elastic string or paper strip.
Tighten without compressing, the string should still slide.
Mark the overlap point with a pen.
Unfold and measure the length with a ruler: the result in millimetres is the size.

Watch out: the string must pass the knuckle, not just the base of the finger. If the knuckle is wider, it sets the minimum size.

The reference ring method

Lay a ring that already fits flat, measure its inner diameter in millimetres, then multiply by 3.14. A 17 mm diameter gives about 53.4, so a size 53 or 54.

The most common traps

Measuring in the morning. Fingers are at their thinnest on waking.
Measuring in cold weather. Cold noticeably reduces finger circumference.
Forgetting the knuckle. A thin base with a wide knuckle means the knuckle sets the size.
Ignoring band width. A wide band feels tighter than a thin one at the same size. Count half a size more above 6 mm of width.
Transposing between fingers. Each finger has its own size, and the dominant hand is often slightly larger.

And adjustable rings

An adjustable ring, open at the back, absorbs one to two sizes of difference. It is the safest option for a gift when the size is unknown. The trade-off: the metal fatigues if it is opened and closed often, especially on thin bands.

Frequently asked questions

How do you find your ring size?

French size equals finger circumference in millimetres. Either a non-elastic string measured with a ruler, or an existing ring’s diameter multiplied by 3.14.

What time of day should you measure your finger?

Late in the day at normal temperature, when the finger is at its usual volume.

What if you are between two sizes?

Take the larger size, correctable with a reducer, except for wide band rings.