Last updated: 3/3/17. Nancy LT Hamilton Author.
Determine your ring size and find the inside diameter of that size.
If you are trying to determine the diameter of your ring size, using a ring sizer, ensure that you measure exactly in the center of the horizontal and vertical lines – otherwise, your measurements will be off (you’ll frequently get different numbers) – especially with plastic sizers.
Even easier, use a chart like this one at RingSizes.Co that tells you what the interior ring dimensions are. Although, you should read about what I discovered about online charts, below.
There are several charts, out there in the interweb world but, of the five, that I surveyed (and I only checked one size – 11), four of them had different numbers from one another. There are international standards set by ISO (a worldwide federation that sets international standards). The standards for ring diameters are found in publication ISO 8653:1986. It costs about $38.00 US. I’ll guess on diameters for now – or use one of the many charts (whether right or not, is anybody’s guess) available online. Just search for: inside ring diameter chart or something like that.
Determine your sheet metal gauge and use a chart, like my B&S Gauge Chart, to determine the size, in mms of your metal gauge.
Add .5mm if the metal used is over 4mm wide.
To figure out your own sizing (instead of using the chart) here’s the formula: (A [inside diameter] + B [metal thickness])* pi . Pi is(3.14159265359+). You can round Pi down to 3.14 if you want. In summary, the formula is: (A + B) * Pi = blank length (+ .5mm if over 4mm wide).
A Observations: Online Charts and Formulas
I, using the chart from RingSizes.co for the interior diameter of my size, calculated the required blank length, using the formula: interior diameter (19.84mm, 19.8 or 19.6mm – depending on whose chart!) + gauge (in mms) x 3.14 (Pi rounded down) + .5mm because of the width and came up with 68.6. One chart says that the interior ring circumference should be 62.33 and the other chart says the interior circumference is 61.33. The third chart said 62.1! So, the diameter measurements are different and, not unsurprisingly, the circumferences are too. It’s no wonder that people find it difficult to make ring blanks the correct size! I give up – for now.
All I know, is that when you make a ring, the interior size is compressed and the exterior of the band is stretched. Knowing this, and looking at the ring blank lengths, the interior circumferences don’t seem right – they seem way too small. I’ll update with the results of my ring blank making and I’ll measure the circumference and diameters too. I’m going to make one ring using the chart and one using the calculation. I’ll report back with my results!
Other Considerations About Ring Sizing
How much metal you remove from the ends, how you mark the metal, how cleanly you cut the metal so, sometimes we need to stretch (or shrink) our ring blanks – all contribute to size variances. This is, just one of the many reasons, why I make adjustable rings. Not only is the sizing iffy but, people’s fingers change size throughout the day, month and year – not to mention over a lifetime!
Related Reference Books
- Jewelers Resource: A Reference of Gems, Metals, Formulas and Terminology for Jewelers (Revised Edition) (Jewelry Crafts) by Bruce Knuth.
- Jewelry Concepts and Technologies by Oppi Untracht.
Or visit my Links: Books page for other great jewelry making books.