The most reliable way to get your Harmony piece made to your exact size is the following:
1- Get a ruler, ideally transparent.
2- Place it on a ring you have got with the desired measure, try to make it as centered as possible.
3- Measure the inside diameter of the ring.
4- That measure, in millimeters, is yours. (1 mm = 0.039 inches, 1 inch= 25.4 mm).
Below we show you a couple of examples:
If you don't have a ring handy for the desired finger, the image below shows how we can measure the size of a ring, with the aid of a tailor tape measure. Placed around our finger phalanx, it will display how many millimeters there are around the finger where we want our ring to be worn.