Unfortunately ring sizes are not measured the same way in every country of the world and there is no real mnemonic aide in order to remember each and every sizing chart. As for bracelet sizes, they may vary from one brand, country, or retailer to another, considering they often apply their very own S/M/L standards. Many would just measure them in centimetres or inches by laying them flat (1 mm equals 0.04 inch). Necklaces vary by length and they are generally chosen to reflect a person's style or preference.
Here is a complete guide to ring, bracelet and necklace sizes for the broad use of both the professionnals and the private people struggling with buying a piece of jewelry in a foreign country!
Jewellers measure one's ring size with a finger gauge and rings themselves with a ring sizer. In addition to the use a gauge, the talented London jeweller Shaun Leane also gives the following very useful advice:
"Measure your ring size at the end of the day when fingers are at their largest. Consider the width of the band, a particularly thick band will feel tighter than a thin band so you may want to buy a full size larger than your normal ring size. Ensure that your ring sizer fits comfortably, snug enough so that it will not fall off, but loose enough to slide over your knuckle."
You should also consider the weather when trying on a ring or sizing your finger. Warm weather make the fingers swell and remember that if you a try a ring when you are pregnant, it might be little too large a few months later. Of course you may have it resized then.
Many jewellers nowadays offer printable ring sizers on which one puts one's own ring the drawn size that fit best. One may also try to measure the inner size of the ring with a string and lay it flat on a ruler in order to get the size only to check it on the below chart, however I would recommend to have your finger measured by a professional just to be sure.
Some rings have adjustable sizes and many techniques exists. Some rings are specifically designed for knuckles with arthritis, so that a health issue doesn't get in the way of wearing rings. Lastly keep in mind that sizing works slightly differently whether you are looking for a large ring or a thin band.
Global Ring Sizing Systems
There are several systems ring sizing in use around the world:
In the United States, Canada and Mexico, ring sizes use a numerical measure, for whole and half sizes. An increase of a full ring size is an increase of 0.032 inch (0.8128 mm) in diametre, or roughly 1/10 inch in inside circumference.
In the United Kingdom, Australia, New Zealand, South Africa and Ireland, the ring sizes are defined using letters in alphabetical order, for full and half ring sizes.
In Japan, India, South America, Korea and China, ring sizes are specified using a numerical measure from 1 to 32. There are no half sizes and sizes are not linked to diameter or circumference.
In Italy, Spain, Netherlands, and Switzerland, ring sizes are specified as the circumference minus 40mm. A 50 ISO was a 10 in Switzerland.
In France and Germany each size corresponds to the inside circumference of a ring in millimeters. Size 52, an average classic female size, means the inside circumference is 52 mm.
If you represent a workshop and you are starting to work for a foreign company, I strongly advise you to ask them to send you a finger gauge from the designated country. Use it as a safe guard and control the ring size prior to delivering the piece.
Here is a very detailed size chart you may use for correspondance study between various countries:
Jewellers measure one's wrists with a bracelet gauge and the bracelet itself with a dedicated mandrel but a private person may use a sewing measure. Alternatively one may use a piece of string or ribbon to measure the size and then carefully lay it flat on a ruler.
The fit depends on the type of bracelet (cuff, bangle, chain bracelet, etc.) but also on the client's choice.. Oftentimes, high jewellery bracelet requires the help of a second person to attach it.
Bracelet sizes generally range from baby size to XXL, but in order to be perfectly sure, one should double it by taking the measure, or wrist circumference, properly in centimetres or inches. One may then choose a loose, fitted or tight wear.
Some particularities apply:
For a cuff bracelet, the fact it is open means you have to remember you can slide it directly on your wrist.
For a bangle bracelet with does not have a clasp, remember to measure the width of the hand as well (fingers pressed together and elongated).
Here is a size chart showing the most common bracelet sizes, bearing in mind that they are not representative of all brands and country habits. Please double-check with the retailer or workshop you are about to buy from.
They are even more trickier!
In France, one could say we have a standard of 40 cm for pendant chains. Fine jewellery makers often add an extra 2 cm with a ring enabling to make it a bit longer.
What is considered is rather the style. Let's consider a choker, a pendant and a long necklace. Their standards length may slightly vary from a maker to another and if you are fond of antiques, one era from another too.