The best way to ensure your ring fits perfectly is to get your finger properly sized. This can be done by visiting any jeweller and asking for your ring size. Most jewellers are happy to help free of charge. Remember to measure the finger you want to wear your ring on, as each finger on each hand varies in size!
Another option is to measure the inside diameter of an existing ring. That measurement equates to a letter. Please follow the link below to determine your ring size.