You can determine the size of the rings in two ways:

Measure the circumference:
Determine the circumference of the ring by using a thread or thread that however, it must be inextensible, measure the circumference of the ring at the place where you would like to wear it. Then measure the thread with a ruler or meter. You need to add at least 1mm or 2mm more to the result you got so that you can easily shoot the ring.

Measure the diameter:
To the ring , which you have at home, measure the inside diameter. You can measure the inside diameter of the ring with an ordinary ruler. However, if you are between two numbers, always choose the larger one.

PATRIZIA 16 17 18 19 20
EU Size 52 54 58 60 63
Inner diameter (mm) 16.5 17.3 18.3 18.9 19.7
Volume (mm) 51.9 54.4 57.6 59.5 62.1