The best way to find out your ring size accurately is by getting a jeweller to help. Most high-street jewellers are happy to do this for you . However, if you can't get to one during the pandemic then you can purchase one of these clever little ring sizer here.
You slide it on like a belt around your finger pull it as tight as is comfortable then check if you are  still able to slip over your knuckle. Read off the letter indicated by the arrow and then let me know and I can make you a beautiful ring!