The Oura Ring 5 Sizing Kit allows for you and those around you to find the ideal fit before purchasing. With a sizing kit purchase, a gift card for the cost of the kit will automatically be applied at checkout. A properly fitting Oura Ring 5 will result in the highest possible data accuracy, comfort, and overall experience. Oura Ring 5 sizes are slightly different from standard ring sizes and other Oura Ring generations. It's important to size yourself and follow sizing instructions. Oura Ring 5 works on all fingers and can be worn on either hand. For optimal accuracy, we recommend wearing on your index, middle, or ring finger.