Here is an easy way to measure an existing ring that fits your finger well.
When ordering a custom ring online to get the exact size you need, you will first download this RING SIZER PRINTABLE PDF at 100% and then double check, with a metric ruler, that the 30mm bar is in fact 30mm.
The image below shows you what the printout will look like.
In that case I would make the ring 1/4 of a size larger... but if you can have your finger measured at a
jewellery store using wide ring measuring bands even better!
"What I need from you is the exact Inside Diameter to create your custom ring!"
Your ring size can change depending upon the width of the ring that you need.
For men’s rings, rings with a width of more than 6mm can require a larger finger size than for narrower widths.
For ladies rings, rings wider than 4mm may require a larger finger size than for narrower widths.
For these reasons you can have your finger size measured by a local jeweler when you are looking to buy a new ring.
Local jewelers by default will use narrow ring bands when measuring your finger size.
If you will be wearing a wider ring (wider than 6mm for men or wider than 4mm for ladies) you should make sure that the local jeweler uses their wide ring measuring bands if they have them available. You should also mention the specific width of the ring that you will be wearing, so that they can advise whether a larger size is needed.
In this image you can see what I mean by the width of a band.