It's quite simple to buy the right size for you. This guide, a tape measure or a calipers it's all you need. For any question or doubt feel free to write to firstname.lastname@example.org :)
The fastest and easier way to know your perfect size is to measure your finger circumference with a tape measure and then to look at "circumference" coloumn below, expressed in centimeters.
The other way - also a good verification of the first method - is to measure one of your rings with a metre or - better - with a calipers. Then, in the following table look at the "diameter" coloumn, expressed in centimeters.
All the data reported for bracelets are inner circumferences expressed in centimeters. The easiest way to know your size is to create a strip of paper as long as the circumference value, or to use a tape measure. Once you have the strip you can make a ring and "test" it easily on your arm. Consider that Cirkuita bracelets are beautiful when weared well fitted but not too tight.
For any doubt, ask advice to email@example.com