I’m often asked how do I calculate how much metal I need to make a ring. A simple calculation that every jewellery maker should know how to implement, and is imperative to making and re-resizing.
To turn up a ring - technical term for making a band it’s a very simple calculation. I’ve heard of people using paid for apps when all you need is a pen, paper and calculator.
Size of ring inner diameter. This example is a UK size M
16.7
+ thickness of metal (eg 2mm)
= 18.7
X Pi (3.14)
So adjust the total length for your filing and cutting. I mark the exact length with my scribe to save me measuring again. An experienced jeweller won’t need to do much other than cut to length.
When resizing a ring and reducing I use the same calculation. Firstly calculate the length of the ring you have to resize. Using the example above I want to resize the ring down to a J.
15.7 + 2 (Size J)
= 17.7
X 3.14
55.7
58.7 -55.7 =3mm to remove from the band.
M to a J
The attached chart will help you with calculating. Always remember to add the thickness of the metal, or the size will be completely wrong. I’ve added US, European and Japanese sizes too. Mine is printed and hung next to my workbench for ease. European is particularly useful for Pandora rings as the size is usually stamped inside the ring.

I’m often asked by students how are the UK ring sizes determined? We use the same system as Ireland and Australia with ring sizes specified using an alphabetical scale with half sizes. After WW2 it was determined that a uniformed scale using half sizes of the inner diameter of 1/64 of an inch would step up in alphabetical order. However, in 1984 it changed with metrication so that one alphabetical size division equals 1.25 mm of circumferential length. For a baseline, ring size C has a circumference of 40 mm.
Ring sizing workshops are easy to book. I offer small group classes or very beneficial one on one classes. For more information please Email me
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