Using a measuring tape is the best and most accurate method to determine your ring size. For the best results, make sure to give enough space to accommodate your knuckle. Keep in mind that your fingers vary in size during the day depending on several factors, like temperature and humidity. Therefore, it is recommended to measure your finger at the end of the day, when it is likely the largest. Also, the same finger might differ in ring size for your left and right hand, make sure to measure the finger that you are planning to wear the ring on.