The Oura Ring Gen 3 sizing ring set allows you to ensure the ideal fit of the ring before purchase. A well-fitting Oura Ring guarantees the best possible accuracy, comfort, and user experience. Oura Ring sizes differ slightly from standard ring sizing, so it is important to measure your size using our tools. The Oura Ring works on any finger and can be worn on either hand. To ensure optimal accuracy, we recommend wearing the Oura Ring on the index finger.