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The correct size depends, not just on the finger, but also on the ring. A wide ring will probably need to be a slightly larger size than a narrow ring. Finger size varies, even over the course of a few days: narrower in cold weather and wider in hot. It can also be affected by health. Like blood pressure readings, the most accurate result is found by taking a series of readings spaced over days and at different times of day.
The following ways of determining size are listed in descending order of reliability.
1. The best way is to visit a jeweler, who is likely to use a set of metal finger gauges such as those shown at right. He or she will also be able to take into account what sort of ring you are thinking of buying. Nowadays, if the intended wearer can't come to the shop, many jewelers give away disposable plastic gauges.
To use a set of finger gauges, try progressively smaller sizes until you come to a size that just won't go on. Then reverse course, trying larger sizes until you reach one that is comfortable.
2. Measure an existing ring that fits well. This method is more accurate if the width of the hoop of the new ring resembles that of the old.
3. (Not recommended) Measure by wrapping a very narrow, somewhat stiff strip of paper around the finger. A better alternative is a plastic cable tie, because you can try slipping it on and off, which you can't do with the paper.
Gauges that you download from the internet and print out can be very misleading. Between the net and the printer output tray are many points at which the computer (and/or printer) may be reducing or enlarging the image.
4. (Not recommended) The worst way is using a string. String is flexible and takes any shape; rings are stiff and nearly circular.
5. Guess. In some situations this is all you can do. Guess big, because it is easier to make a ring smaller than bigger. Women's ring fingers typically take a U.S. size 6 to 7. Or, arrange with the jeweler to exchange the ring for the right size after you have popped the question (but many women will not want to give up the very ring you proposed with).
Some people have fingers that taper gradually from palm to fingertip; it is hard for them to retain a ring.
A competent jeweler can resize most rings, and the resizing will be invisible to the naked eye. Success depends in part on what the ring is made of. Plain gold bands are the easiest rings to resize. White gold has often been plated with rhodium, perhaps with plated layers of other metals, such as nickel, beneath. It can be very difficult to replate the ring to match the original plating. Silver, because it is often rhodium-plated, can be problematical for the same reason. Platinum requires extremely high temperatures. Stainless steel and titanium rings are difficult or impossible to resize. Some rings cannot be enlarged because they contain an inset stone that would be stressed and possibly crack in use if the hoop were enlarged.
The technique used to resize the ring partly depends on how large a change is needed. If it is only a ¼ or ½ step (US sizes), machines exist that can actually stretch or compress the band, assuming there are no stones. Rings whose cross section varies widely cannot be stretched, because all the thinning would be concentrated in the parts of the band that are already thinnest. A technique often used on rings with stones involves a machine that uses rollers to roll out and thus lengthen the part of the band without stones. All these techniques unavoidably thin the band somewhat.
If a greater change in size is required, the shank will be cut and a section removed or a new section inserted. This is not as alarming as it sounds. In fact, a great many rings are manufactured with a join in the first place, and the jeweler will open the shank at the same point.
To enlarge a ring, the shank is cut and a piece of new stock is soldered in place. If the ring has been previously resized larger and already has two joins, the jeweler will remove the previously inserted piece and insert in its place a new, longer piece. The resized ring will thus continue to have two and only two, joins. The quality depends on workmanship (how well the cut ends were rendered plane, parallel, and aligned), and upon how closely the metal of the new piece matches the original alloy used in the ring. A large shop is likely to have a greater selection of alloys than a small one.
In the latest equipment, a laser substitutes for the torch, and solder is unnecessary. The heat is so intense and focused that the metal melts and flows together.
When picking up a resized ring, examine it closely. It should of course be clean, completely free of the abrasives used in repolishing. Other than that, on examining both the inside and outside surfaces, you simply don't want to be able to tell the ring was resized. That means the shank has a uniform, consistent shape and color, and there are no pitmarks or other depressions to reveal the location of the join. And it should fit. If there is any doubt in your mind that the size specified has been achieved, ask if you may test the ring on the jeweler's tapered steel mandrel.
Advice on resizing from a seller of titanium rings. Notice their offer to replace a newly-bought ring with one of a different size.
Download and print the chart. Even if you do not need to convert between the different national ring sizing systems, the chart is an easy way to read off inside circumference and diameter in inches and millimeters.
To convert a size in one system to a size in another, look up the circumference in millimeters of the size that fits. Then find the smallest size in the system you wish to convert to that has a circumference at least equal to the first circumference.
Quarter-sizes (for example, 6¾), intermediate between the whole and half sizes, are also used, and sometimes even eighth sizes (e.g., 6 5/8).
The origin of American ring sizes is unknown. A U.S. patent for a ring gage, issued to F. E. Allen on February 3, 1874, shows ring sizes from 1 to 13 with quarter sizes, so the system was in use by then. In the 1920's the National Bureau of Standards surveyed the ring gages¹ in use at a nationwide sample of jewelers and discovered the same size numbers were being used for different dimensions. This appears still to be the case.
1. U.S. Dept. of Commerce, National Bureau of Standards.
Jeweler's and Silversmith's Weights and Measures (2nd ed).
Bureau of Standards Circular 43.
Washington, D.C.: U. S. Government Printing Office, 1921.
The earliest British scale appears to have had steps of 1/64th inch in diameter, but the 1949 British Standard had a whole size steps of 0.0155 inch of diameter (1/64th inch is 0.015625 inch). Some sources say the scale begins at 0 = an inside diameter of 0.4595 inch.
A new standard was issued in 1987. It retained the names of the sizes but otherwise was more European: millimeters instead of inches, and circumference, not diameter. Each whole step is an increase of 1.25 mm in circumference. The largest difference between the old and new scales is 0.0051 inches, which is negligible.
British Standard BS6820:1987.
British Standard BS1283:1945.
Jewellers' ring sticks and ring gauges.
This standard is withdrawn.
The scale begins at 0 = an inside diameter of 13 millimeters; a whole size step is an increase of one-third of a millimeter in diameter.
In the most common system, the size is simply the inner circumference in millimeters; typical sizes fall roughly in the range 38 to 69.
The size is the inner circumference in millimeters. Half and quarter fractional steps are used.
An older German system, in whole, half and quarter steps running from about 13¼ to 22, was simply the inner diameter in millimeters.
The most popular ring size system in Poland starts with size 1 at 12.666 millimeters and increases in increments of 1/3 millimeter. So size 1 is 12.666 mm, size 2 is 13.00 mm and so on. Size 33 is 23.33 mm.
The inner circumference in millimeters, minus 40.
Yet other sources describe the Swiss sizes as the inner diameter in millimeters plus 40. If you have personal knowledge of Swiss ring sizes, please write us.
Antoinette Mattias and Antonio C. Bonanno.
Engagement & Wedding Rings. 3rd Ed.
Woodstock (VT): GemStone Press, 2003.
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Last revised: 19 May 2016.