Ring sizing is a tricky one. If you are unable to visit Amanda at her studio to have your finger measured, then pop into your local jewellers and ask them if they can do it for you. Most Jewellers will be happy to oblige.
In the UK we use letters, but different countries use other references, mostly numbers. There is a size conversion chart
here.
Alternatively download the easy to use ring sizer below and follow the instructions. This will give you a ring sizing belt to wrap around your finger, or if you have an exciting ring simply lay that over the circles to find your size.