Here you have two simple options.
Option 1: Choose a ring that suits you and measure its internal diameter. When you have the measure, check here the equivalence with our sizes.
In case of being between two sizes, we recommend you to choose the bigger one.
Option 2: Print our size guide on an A4 sheet and follow the instructions carefully to ensure that the size you are going to select is the right one for you.
Please contact us for more information, and we will help you.